One of the most morbid rumors is spread by Miss Stephanie Crawford, the leading town gossip. Jem receives information from Miss Stephanie that in Boo's younger days, he sat in the living room cutting papers with scissors when his father walked by:
As Mr. Radley passed by, Boo drove the scissors into his parent's leg, pulled them out, wiped them on his pants, and resumed his activities.
While it is true that the family keeps Boo locked away in their home, and he never emerges (which is the source of endless fascination for the kids), one has to consider the veracity of any information spread by Miss Stephanie.
Miss Maudie's attitude toward Miss Stephanie's rumors about Boo is pretty much perfection:
Stephanie Crawford even told me once she woke up in the middle of the night and found him looking in the window at her. I said what did you do, Stephanie, move over in the bed and make room for him? That shut her up for a while.
Miss Maudie is a rational woman who doesn't align herself with the swaying opinions of the town. Thus, she shows that she doesn't really believe the rumors about Boo, and certainly not those propelled by Miss Stephanie.
Still, the children continue in their efforts to draw Boo out of his house and into their realm of entertainment. When they concoct a plan to deliver a note to him, they promise him ice cream to help him "feel better," because, as Dill says,
How'd you feel if you'd been shut up for a hundred years with nothin' but cats to eat?
It's unclear if Dill is using a hyperbole referencing how long Boo has been inside or whether he really believes him to be over a hundred years old; the legend and mystery just keep growing. But somehow, Dill has seen or heard a rumor about Boo's diet consisting only of cats.
By the end of the novel, Scout comes to realize that perhaps Boo looks around at their society and has some strong reasons for avoiding interactions with people, as the mystery of the man shrinks just a bit.