The laugh comes from Bellboy Donald, a Donald Duck cartoon released in 1942, where the small, mischievous laugh fits a character enjoying a sly moment. It later entered the Hollywood Edge sound library as a catalogued effect for a little man or kid laughing rapidly, which helped it travel far beyond its original cartoon. Editors now reuse it as a compact shorthand for sneaky delight, because a fraction of a second is enough to signal that a character is up to no good.