"That mousetrap is a portable tool for capturing small animals alive."

— Sigint

The mousetrap is an item Naked Snake uses during the Virtuous Mission and Operation Snake Eater. It is used to catch food alive, such as snakes, birds, frogs, and other animals Snake encounters on his missions. It must be used to catch the invisible Tsuchinoko. In addition, the mousetrap requires bait for it to work. However, once it is used and activated by one of the animals, there won't be any bait left, thus requiring Snake to recover them once used. Major Ocelot of the elite Spetsnaz GRU unit, the Ocelot Unit, also carried a mousetrap on his person. They can be seen on the Map once placed. It weighs 0.4 kg.

Colonel Campbell will also remark if the player kills several rats that he doesn't need a rattrap before irritably reminding Snake that they need someone to stop the Sons of Big Boss from launching a nuke.

"A trap equipped with bait to lure small animals and capture them alive."

— Mousetrap description in Metal Gear Solid 3: Snake Eater