What does Tom do to the person who hears them? What does that person say happened as a result of this trick?

Tom and Huck climb into the house and steal three candles, for which they leave a nickel as "pay". Then Tom quietly makes his way to Jim, takes off Jim's hat, and places it on a tree branch above Jim's head. He soon returns and tells Huck what he did.

After Jim wakes up, he believes he has been bewitched, and keeps the nickel as a token around his neck for the rest of his life. According to Huck, Jim tells all the other slaves that he had been ridden around the world by some witches, and that the nickel was given to him by the devil.