This article lists the secrets in Metal Gear Solid.
- Near the beginning of the game, while crawling through the ventilation ducts to meet up with the DARPA Chief, look into the vent before the Chief's to get a first glimpse at Meryl Silverburgh doing sit-ups. If the player leaves and re-enters the vent, she will perform leg stretches and push-ups. On the fourth time, Meryl will repeat the same exercises in her panties.
- In The Twin Snakes, the player only needs to crawl backwards to the back of the vent for the game to load a different exercise animation. If the player leaves and re-enters the vent once, Meryl will be in her panties.
- If the player does not acquire the SOCOM before meeting Meryl in the cells, Solid Snake will hold the tip of her FAMAS with his hand, rather than draw his SOCOM.
- If the player rushes into the ladies bathroom in close pursuit of Meryl, who is disguised as a Genome Soldier, she will be wearing her panties in the following cutscene, because she didn't have enough time to put on her pants.
- After locating Meryl in the Warhead Storage Building, looking at her in First Person View for an extended period of time will cause her to blush and comment.
- If the player hits Meryl, she will slap Snake in retaliation. If the player does this at the end of the Canyon, she will whistle for a wolf dog to attack instead.
- When Meryl is being controlled by Psycho Mantis, pressing the First Person View button will show the view through Psycho Mantis' eyes, although it will still appear as though Snake's on the radar.
- Shooting Meryl after she has been shot by Sniper Wolf will provoke angry responses from Roy Campbell and Naomi Hunter.
- The number of times that Revolver Ocelot administers an electric shock to Snake is dependent on the difficulty level set for the game:
- Easy: 3 "Had enough yet? We're not finished yet!"
- Normal: 4 "You're still okay? Want me to go on? Can you take one more?"
- Hard: 5 "Give up. Make it easy on yourself. One more time!"
- Extreme: 6 "Come on! You don't want to die like this, do you? I can do this all day!"
- In The Twin Snakes, the set number of shocks is always three. Ocelot can, however, be heard saying "Can you take one more?" in the first teaser trailer for the game.
- If the player makes some noise in the holding cell or presses the Circle button to perform a combo, Johnny Sasaki will say "Shut up!" or "Shut up in there, willya!" If the player crawls under the bed while he's still standing guard, Johnny will ask, "What the hell are you doing?" If the player uses ketchup, Johnny will instead ask, "What are you playing around with that ketchup for?" and laugh.
- Gray Fox will come to Snake's rescue (by slashing the lock in Metal Gear Solid and slicing the door in half for The Twin Snakes) if Snake doesn't hide under the bed or use the ketchup.
- After escaping from the cell, if the player does not knock Johnny out, he will chase them. Ignore and don't attack him; when the player runs through the doors that leads into the torture room, a short sequence will begin where Johnny suddenly has another bout of diarrhea and rushes for the toilet. If the player knocks on the door, Johnny will groan in pain.
- If the player keeps calling Mei Ling and chooses "DO NOT SAVE," she will tell them to stop calling her on the third call. On the fourth call, she will say nothing and prompts the player to save or not. Choose not to save again. Call her and choose not to save once more. On the sixth call, she will stick her tongue out and close the channel without prompting to save.
- If the player keeps calling Nastasha Romanenko, she will eventually tell them about her past, and what happened to her parents, which led to her hate for nuclear weapons.
- Every time the player finishes a boss battle or complete a significant event, some members of the support crew (via the Codec) will reveal their thoughts on the matter.
- Calling people while holding some items will drum up an interesting conversation.
- Naomi and Mei Ling will lecture Snake while he has his cigarettes equipped. Nastasha won't have a problem at all if the player calls her since she smokes too.
- Calling Campbell when the player acquires any kind of weapon will prompt him to state how to use the weapon. If they haven't already called Nastasha, he will tell them Nastasha's frequency.
- Calling Campbell, Otacon, or Master Miller, while in the women's bathroom will prompt them to tell Snake to continue his search for Meryl. Calling Nastasha will cause her to be annoyed with him. Calling Mei Ling will cause her to angrily refer to Snake as a pervert.
- Call Campbell four times during the Psycho Mantis battle. On the fourth call, he will tell the player the secret to defeating Mantis. If they then die without changing controller ports, he will tell them the other secret to defeating Mantis.
- During boss fights, different characters will give the player tips and information.
- Calling Campbell and Naomi will give a detailed background on the current FOXHOUND member.
- Shooting the rats near the Comm Towers and in the Blast Furnace will prompt different responses from Snake's teammates.
- Killing the ravens before the boss fight with Raven will provoke the same kind of responses; Miller will also correct Snake who calls them crows. Additionally, Raven will be given an extra line when he meets Snake.
- All references to the "crows" will also be changed to "ravens" if Snake calls Miller first.
- Calling Master Miller before he tells Snake that Naomi might be an enemy spy will lead to Miller giving a short lecture on northern ravens and reciting a verse from a poem written by English poet Christopher Marlowe. He'll then say "By the way..." and the normal conversation about Naomi will begin.
- Call Master Miller while walking on a noisy floor. In the PlayStation version, he tells Snake to try "fitting his socks over his shoes" after Snake expresses his frustration trying to walk stealthily. The line is changed in the remake, however.
- If the player waits a while to throw away Ocelot's timer bomb, Deepthroat will eventually call Snake at about 15 seconds to go and warn him about the bomb in his equipment.
- In The Twin Snakes, Deepthroat calls much sooner. If the player then continues to wait, Colonel Campbell will then call Snake and tell him how to throw the bomb away.
- In the PlayStation version of Metal Gear Solid: Integral, there are two hidden Codec frequencies: 140.07 and 140.66. 140.66 plays classic Metal Gear themes at certain areas, including "Discovery", "Zanzibar Breeze", and "Theme of Solid Snake." 140.07 features staff commentaries (in Japanese only).
Otacon's stealth camouflage will be available on the player's second playthrough if they submit to Ocelot's torture; if they successfully resist the torture, they will instead get the bandana, which gives Snake unlimited ammo for all weapons. The Camera can be found in the Armory South.
On the third playthrough, Snake will be wearing a tuxedo, which is an obvious homage to the James Bond series. Also, Gray Fox will have a different color palette on his exoskeleton, changing to red and gray. In Metal Gear Solid: Integral and The Twin Snakes, Meryl will also be wearing a Sneaking Suit.
The jingle that plays when the Konami logo appears is actually taken from "End of the Dark," the theme music from Hideo Kojima's previous game, Policenauts, which was released by Konami in Japan for the following four platforms; the NEC PC-9821, the 3DO Interactive Multiplayer, the PlayStation and Sega Saturn. As well as the jingle, there are various posters scattered around in the PlayStation version, and the sequence when Otacon talks about anime is the EMPS takeoff scene from Act 3 of Policenauts. The game, which Kojima has said to be the most exhausting game he has ever written/directed. It is also the first game that Yoji Shinkawa ever worked on, first as a debugger in the PC98 version, before taking over as art direction in the console versions of the game.
After going through the wolf cavern for the first time, Meryl will be on the other side waiting for the player. Equip one of the cardboard boxes so that it is ready to go with quick-change. Hit Meryl, then quickly equip the cardboard box. She'll whistle to call the wolves to attack the player, but instead, the wolf pup will urinate on the box. The advantage here is that when crossing the cavern later in the game, if the player is wearing the box, the wolves won't attack them.
After beating Sniper Wolf a second time, leave to the area where the player must insert Disc 2. Then return to the snowfield. Wolf's body will be gone and a wolf pup will be in her place.
On the right side of the snowfield near the ration, pressing Snake against the hill will pan the camera out to reveal a parachute spread out on a tree. A short Codec conversation will follow, where Snake and Campbell debate whether it belongs to Liquid, with Snake concluding that Liquid couldn't possibly have ejected from the Hind D (helicopters with ejection systems require specialized explosive bolts to detach the rotors) and must have left the parachute deliberately to show Snake he was still alive.
- When the player meets Psycho Mantis, the game looks through their memory card for saves from other Konami games. Mantis will then make comments referencing those games.
The following game saves provoke responses:
- Castlevania: Symphony of the Night
- Policenauts (Japanese version only)
- Azure Dreams
- Snatcher (Japanese version only)
- Tokimeki Memorial (Japanese version only)
- Vandal Hearts
In the Japanese version, if the player has save files from both: Snatcher and Policenauts, it will trigger the following message:
- Psycho Mantis: "So you like Kojima's works?" (小島作品が好きようだな？ Kojima-sakuhin ga suki yō da na??)
- Hideo Kojima (v.o.): "Thank you for your continuing support..." (いつも応援してくれありがとう… Itsumo ōen-shitekure arigatō...?)
In The Twin Snakes, the game will read off these savefiles:
- Eternal Darkness: Sanity's Requiem
- Super Mario Sunshine
- Super Smash Bros. Melee
- The Legend of Zelda: The Wind Waker
If the player has none of these games saved in their memory card in both versions, Mantis will say their memory is completely clean.
- If the player presses the first person view button during the boss fight with Mantis, it will show the view through Mantis' eyes.
- Shooting the bandages off one of the Mantis busts will make Mantis unable to read the player's mind if they happen to not be using another controller port. This actually simply destroys the statue's head, and only works if Campbell has already suggested it; he will do this if the player have already called him enough times for him to tell them to "use the controller port" but died afterwards without switching ports.
- During the first part of the boss battle with Psycho Mantis, he will scream "Blackout!", and it will look like the player's TV has switched channel. However, on the top right screen, it will say "HIDEO," rather than "VIDEO."
Before the fight against Mantis in The Twin Snakes, there will be three pictures of real life people, with Ryuhei Kitamura on the left, Hideo Kojima in the middle and Denis Dyack on the right.
- After moving the controller, the three pictures will laugh in high-pitched voices after Mantis laughs.
- When Mantis covers much the room with fire, the picture on the right will have caught fire. The man in the picture will also have his face burned off, with muscle showing. The picture of Kojima will also look at him.
Once the player has the camera in their possession, photos can be taken of the game staff in certain locations, styled to look like ghosts. There are 42 of them hidden throughout the game:
- Unconscious Johnny outside Meryl's jail cell (Masayuki Kobayashi).
- Corpse of ArmsTech president Baker (Nobuyoshi Nishimura).
- The cliffs of the heliport (Tomokazu Fukushima).
- Corpse of Sniper Wolf (Jeremy Blaustein).
- Policenauts/Zone of the Enders poster (Hideo Kojima).
- Electrified floor (Daizo Shikama).
- Holographic model of the Comm Towers in the commander's room (Dennis Dyack);.
- Hallway of corpses, outside Otacon's lab (Yoshikazu Matsuhana).
- Roof destroyed by Hind D in communications tower A, before going over the side on the rope (Kumi Sato).
- Meryl's blood stains in the underground passage (Ikuya Nakamura).
- Outside comm tower A, on the upper walkway where Sniper Wolf was shooting from (Yoji Shinkawa).
- Cargo elevator to the warehouse (Vulcan Raven boss battle) (Kazunobu Uehara).
- Sewage waterfall, prior to Metal Gear's maintenance base (Yutaka Negishi).
- During the fight with Metal Gear (Takashi Mizutani).
- Men's restroom (Yuji Korekado).
- Picture frames in the Commander's Room (Hideki Sasaki).
- Torture machine (Makoto Sonoyama).
- Container in the middle of Vulcan Raven's warehouse (So Toyota).
- Watertank-like structure in the canyon (Shigehisa Kozyou).
- First crawling point in wolf dogs caves (Yoriko Shimizu).
- The mirror located in women's restroom (Yukiko Kaneda).
- Broken glass at the edge of Otacon's lab (Yumi Takade).
- Elevator in the comm tower B complex (Ikuzo Fujimura).
- Tip of Metal Gear's rail gun, in its underground base (Mineshi Kimura).
- Rock in canyon (Yoshiteru Kobayashi).
- Corpse of the real DARPA Chief in cell (Shigeo Okajima).
- Reflection in wolfdog cave puddle (Shiro Mukaide).
- Pillar where ArmsTech President Baker is tied up (Kohei Onoda).
- Corpse of Decoy Octopus/fake DARPA Chief (Takashi Kitao).
- Dead end of air duct (Ryoko Yoshimura).
- Water at cargo dock, at the beginning of the game (Kazuki Muraoka).
- Top of heliport building (Takanari Ishiyama).
- Elevator to tank hangar (Miki Ito).
- Bridge on the blast furnace (Motoyuki Yoshioka).
- Deep in the shaft of comm tower B top level (Satoshi Hirano).
- Lowest point of comm tower B elevator (Motosada Mori).
- Dark area of comm tower A stairs (Takashi Kinbara).
- Dead end of the steam room, in the blast furnace (Hiroyuki Togo).
- Hidden armory store room behind the weakened wall (Ryoji Makimura).
- Metal Gear observation room (Ichiro Kutome).
- Sleeping soldier in the heliport (Nobumitsu Tanaka).
- Stairs in the heliport (Kenichiro Shigeno).
- Tip of nuclear warhead in the nuke storage area (Shinji Yamashita).
- Way down in the dark from the walkway between comm towers A and B (Scott Dolph).
The ghosts can be removed from the photos be selecting "Exorcise" in the main menu browser. Additionally, the guard who shows signs of life in the corridor leading to Otacon's lab, can also be exorcised from photos.
If the player calls Campbell during the Hind D fight, he will advise him to listen for the sound of the rotor blades to tell where the Hind is. If the game sound is set to mono, however, Campbell, Naomi and Mei Ling will express confusion that Snake doesn't own a stereo television. Campbell, however, reassures Snake that he can still beat the Hind without the use of a stereo TV.
At some points in the game, different lines of dialogue will be said under certain conditions:
- If Snake takes too long to board the elevator down at the cargo dock, Campbell will note that Snake was a little slow.
- If the player has not done any VR training, Snake's line about training will be omitted.
- If Snake is discovered by sentries in the first area of the game, another cutscene will be activated if Snake goes through the second floor ventilation shaft where two guards talk about "another" intruder.
- If the player takes too many tries to defeat Ocelot, Ocelot will make fun of Snake, telling him that he'll never live up to the name of the Boss (Big Boss). Ocelot will also have a different response when Gray Fox severs his hand.
- If the player has not saved in a long time prior to the torture sequence, an extra line is added in which Ocelot will comment, "You really wanna travel down that long road again?"
- Snake's response to Otacon upon using the ketchup will be different depending on whether it worked or it either didn't work or simply wasn't used.
- At the end of the game, if Snake and Otacon ride off on the snowmobile together, Snake will tell Otacon that his real name is David, to which Otacon replies, "I'm Hal, Dave." Snake then comments that Hal and Dave make a great pair and laughs, referencing the movie 2001: A Space Odyssey. He then makes the suggestion that they should take a trip to Jupiter.
Alternate Game Over dialogue
- During the boss fight with Ocelot, if the player kills Baker, Ocelot will call them an idiot.
- If the player dies during the torture sequence, Liquid will angrily say, "Ocelot, you did it again" (referring to Donald Anderson's death). Ocelot will then apologize.
- If Snake kills Meryl during the boss fight with Mantis, Snake will somberly say, "Meryl..."
- If the player hits Meryl, she will slap Snake and take a small part of his health. If she kills Snake, Mei Ling will say, "This can't be."
- If the timer during the battle with Liquid reaches zero, Liquid will laugh maniacally.
Alternate boss fight methods
- During the boss fight with Gray Fox, the player can use chaff grenades to render him motionless.
- During the second boss fight with Wolf, the player can use the Nikita or the Stinger to defeat her. The player can also use the Nikita to defeat Raven during his boss fight.
- During the second boss fight with Metal Gear REX, it is possible to use the PSG1 to defeat Liquid.
- It is possible to defeat Psycho Mantis in the original Metal Gear Solid without switching controller ports on a second playthrough with the bandana. If the player shoots the FAMAS until the magazine bullet count is low, the bullets will become tracers. If the bandana is equipped at this point, the FAMAS will shoot endless tracers. These tracers may register as hits despite Mantis's efforts to dodge them. However, he will still comment on "[the player using] the other..." upon his defeat even if the controller port was never switched.
- In the warhead storage building B2, "Hal's Lab" is scrawled on the door leading to Hal Emmerich's laboratory. This may be a reference to HAL Labs, where Kojima's close friend and game designer Masahiro Sakurai formerly worked.
- Inside "Hal's Lab", a Net Yaroze edition PlayStation with a DualShock controller can be seen in the middle part of the lab. For the remake, it is replaced with a GameCube and a Wavebird controller. Statuettes of Mario and Yoshi can also be seen sitting on the console in the upper-right corner. Shooting Mario's statuette will result in replenishing Snake's health (accompanied by the standard 1 Up sound effect and animation).
- Sometimes when Snake has to recover the PAL key, he will discover that a rat has eaten it. To get it back, he will have to kill it by shooting it or blowing it up with C4.
- In The Twin Snakes, there is a small catwalk area with a steam pipe and a liquid nitrogen pipe. These can be used to shorten the length of time it takes to activate Metal Gear REX by simply shooting the pipe with the key equipped.
The Konami trademark Easter Island head can be seen in the second room of the hallway in the B2 Warhead Storage.
The crane in the Blast Furnace can be damaged with either the Nikita or Stinger missiles, allowing for easier access to the other side.