The Prison Dog is a character from Pirates of the Caribbean, originating in the original theme park attractions in which he is seen holding keys in his mouth near some imprisoned pirates, who attempt to lure the animal closer to no apparent avail.
The scene is recreated in Pirates of the Caribbean: The Curse of the Black Pearl, and the dog makes further appearances in Pirates of the Caribbean: Dead Man's Chest, and Pirates of the Caribbean: At World's End.
The prison dog is the keeper of the keys to the jail in Port Royal, he carries the keys in his mouth, the prisoners vainly trying to get the keys. The dog appears again in Dead Man's Chest with Pintel and Ragetti after they have escaped prison and are headed for Pelegosto to search for the Black Pearl. He was named "Poochie" by Pintel until he was left on Pelegosto. Later he was chased by cannibals. In a post-credits scene, it is revealed that the dog becomes the chief of the Pelegosto tribe.
In Pirates of the Caribbean: At World's End, the dog is the keeper of the Pirata Codex keys on Shipwreck Island. Captain Teague explains the dog's presence by saying, "Sea turtles, mate," a reference to Jack Sparrow's tale of his own escape from being marooned.