What prank does Huck play on Jim, and how does it backfire>

Huck Finn in "The Adventures of Huckleberry Finn" by Mark Twain is a prankster. He is free and full of mischief. Jim, the slave who escapes with Huck, is very superstitious. Jim is afraid to ponder about a dead man they find. He is also afraid to touch the skin of a snake that has been shed. He believes it causes bad luck. Huck finds a rattle snake and kills it. He thinks it will be funny to curl it up and place it on Jim's blanket.

"I killed him, and curled him up on the foot of Jim's blanket, ever so natural, thinking there'd be some fun. "(49)

The joke backfires because the rattlesnake's mate gets in Jim's blanket and bites Jim. He gets bit on the heel.