Why did Huckleberry Finn and Tom go to the graveyard

Tom and Huck have this bizarre notion that you can cure warts using a dead cat. Apparently, what you need to do is take a dead cat to a graveyard one night, say a few words of mumbo-jumbo over a freshly-dug grave, and then throw the kitty corpse after the dead man's spirit. Tom and Huck have never actually tried out this weird experiment, but they're itching to give it a try. Hence their hanging around the graveyard that night.
Unfortunately, the two boys get a whole lot more than they'd bargained for. When they get to the graveyard, they see Dr. Robinson accompanied by Muff Potter and Injun Joe. It seems that they're involved in grave robbing, a very serious offense at that time. As an increasingly scared Tom and Huck look on from behind an old gravestone, the would-be grave-robbers get into a fight. In the ensuing scuffle, Dr. Robinson hits Muff Potter over the head, knocking him out cold. The doctor is then brutally stabbed to death by Injun Joe, who quickly flees the scene, leaving poor old Muff to take the rap for Dr. Robinson's murder.