When Jack Sparrow is stranded inside Davy Jones' Locker, in At World's End, he is there alone (if we exclude any of his clones) with the Black Pearl on a desert.
He finds a mysterious moving rock, and throws it away. The rock turns out to be some sort of disguised crab and runs off. It fetches hundreds of other crabs, and they all come together to help bring the Pearl back to shore.
What are these crabs? I believe they must have some sort of symbolic meaning (e.g., they are the souls of other lost sailors that gave up going back to sea inside the locker), but I don't really have anything to go on aside from pure speculation.