To kill a Mockingbird

This depends on at what point in the story you are referring to. In the early chapters they imagine Boo is a reclusive monster who walks the night.

"Boo was about six-and-a-half feet tall, judging from his tracks; he dined on raw squirrels and any cats he could catch, that's why his hands were bloodstained—if you ate an animal raw, you could never wash the blood off. There was a long jagged scar that ran across his face; what teeth he had were yellow and rotten; his eyes popped, and he drooled most of the time."