What superstition about the dog do Tom and Huck believe? Why is the fact that the dog has his back to them a good thing?

fter they bury the contract, Huck and Tom hear a dog howling ­ a sign that death is coming, according to black slaves' tales. Still afraid for their lives, the boys let out a sigh when they realize the stray dog is howling directly at Muff Potter. After Tom and Huck say good-bye, Tom sneaks back into his bed through the window, unaware that Sid is wide awake.