- The song is heard playing in the conversation between two women tape that Cécile Cosima Caminades recorded and got captured for, something that even indirectly noted by Vladimir Aleksandrovich Zadornov during his briefing to Snake when playing the tape.
- The three primary AI weapons, exempting Peace Walker, as well as Metal Gear ZEKE utilized stanzas of this song in a high-pitched manner when attacking. In addition, with the exception of The Boss AI, all of the AI pods when accessed will have the high-pitched version playing in the background.
- Cécile mentions to Snake that she heard the second female voice "singing a strange song" whilst imprisoned by Strangelove upon Snake finding her.
- The studio/single version is heard in Strangelove's lab when Strangelove first shows Snake the Basilisk pod, playing on offscreen speakers/the PA.
- The same version is heard again when Strangelove tortures Snake, playing on a radio.
- The Basilisk sings it in the climax of the game in Peace Walker Battle 3, just after recovering. The listening characters speculate that this represents The Boss' original principles, "singing" instead of fighting, as it drowns itself in the lake to stop the signal.
- It is lastly played in the first credits sequence, though not in full, being interrupted by radio static.
"Sing" was a popular single a year and a half prior to the Peace Walker Incident, and was featured prominently with Strangelove. When she appeared, it was often played on hardware that allowed selective music playing, which suggests that it was a favorite song of hers.
In the novelization for the game, Sing was replaced with "Imagine" by John Lennon.