Donkey is a musical theme composed by Klaus Badelt (with Hans Zimmer's assistance) for Pirates of the Caribbean: The Curse of the Black Pearl. It appears as track five on the film's complete soundtrack.
The track begins with a funny tune, and then transfers into an amusing and exciting climax (00:27), leading to the end of the track.
In the film
This track is played when Jack, running away from James Norrington's marines, enters J. Brown's blacksmith shop, and tries to break the chains. That's when he burns the donkey's butt, which explains the track's title.