What strange thing happened when Jem lost his pants at the Radleys?
When Jem went back to retrieve his pants, he got quite a shock. His pants were neatly folded and left on the fence. And, the rip had been roughly mended. That meant that someone (probably Boo) had gone outside, seen the pants, and went to the trouble of fixing them. That would be an early indication that Boo (certainly not Nathan) was a kind person who kept his eye on the Finch children. It would scare Jem, but possibly put the idea in his head that Boo was not the animal-eating, father-stabbing maniac that rumor had painted him. As other events unfold, the Finch child no longer regard Boo with fear as much as curiosity.