The gulp comes from the classic MGM Tom and Jerry cartoons, where Jerry the mouse often reacted to Tom's traps and chases with small, exaggerated cartoon sounds rather than words. Short clips like this one were later lifted for soundboards and meme edits because they are instantly recognisable even without the picture. At under half a second long, it is easy to drop into a video, and its nervous, comic swallow still works today because audiences know the character and the old cartoon style behind it.