Jem and Scout both visualize Boo Radley as some kind of terrible ghoul during the early stages of the book. The townspeople generally blame Boo for every kind of unexplained nocturnal activity in the town, from peeping in people's windows to killing cats and eating squirrels. Jem imaginatively describes what he thinks Boo must look like.
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... 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. (Chapter 1)
When Scout finally sees Boo for himself after he has rescued the children from the clutches of Bob Ewell, she discovers a much different person. Boo had
... white hands, sickly white hands that had never seen the sun, so white they stood out garishly against the dull cream wall in the dim light of Jem's room.
(He wore) sand-stained khaki pants; my eyes traveled up his thin frame to his torn denim shirt. His face was as white as his hands but for a shadow on his jutting chin. His cheeks were thin to hollowness; his mouth was wide...and his eyes were so colorless I thought he was blind. His hair was dead and thin, almost feathery on top of his head.
Despite his ghostly looks, Scout quickly came to realize that he was the man who had come to her rescue, and that he was not only her neighbor, but her friend. Scout felt a tinge of guilt that Boo had given her and Jem so much, and that they "had given him nothing, and it made me sad."