The sound comes from S.T.A.L.K.E.R., the survival shooter series by GSC Game World that began with Shadow of Chernobyl in 2007 and is set in the Chernobyl Exclusion Zone. Medkits are a core survival item in the games, used to restore health after radiation, mutant attacks and gunfights, so players know the use sound immediately. As clips and edits from the series spread online, the short effect was shared on its own as a recognisable healing cue for other games and memes.