The clip is taken from Escape from Tarkov, the hardcore shooter by Battlestate Games, where USEC is one of the two playable PMC factions. USEC 3 refers to one of the English voice sets for those operators, whose effort, pain and breathing sounds play in game when a character is hurt, winded or suffering status effects. Players ripped and shared these isolated vocal effects for soundboards and edits, because separated from the gunfire they work as a clear, game-accurate shorthand for being badly injured.