Boo Radley is a mysterious character in Harper Lee's To Kill a Mockingbird. The Radleys live next door to the Finches, Jem and Scout, and they are a very private family. The town is full of speculation about the Radley's son, Boo, because anything that is a little mysterious is material for gossip in Maycomb.
Jem and Scout (and Dill, of course) have fabricated all kinds of stories about Boo, though they really know nothing about him. They regularly enact plays and dare one another to do things at the Radleys. Once Scout hears someone laughing quietly when she gets just a little too close to the Radley house, and once Jem sees (or thinks he sees) a curtain part in one of the windows. We also know that Boo is the one who sewed Jem's pants and brings Scout a blanket on the night of the fire.
"Two live oaks stood at the edge of the Radley lot; their roots reached out into the sideroad and made it bumpy." One day on the way home from school, Scout's attention is drawn to the knot in one of the trees and she discovers two sticks of gum wrapped in their silver foil. She grabs it and takes it to her front porch.
The gum looked fresh. I sniffed it and it smelled all right. I licked it and waited for a while. When I did not die I crammed it into my mouth: Wrigley’s Double-Mint.
When he gets home, Jem scolds her and makes her spit it out because, of course, everyone knows that everything on the Radley place is poisonous. This is only the first gift which Boo Radley is obviously leaving for his two neighbor children. Over time, they discover more gifts. Next is a small ring-box covered with bits of tinfoil from chewing gum; inside are two shiny Indian-head pennies. Then comes a ball of twine which they leave for several days to make sure no one is simply storing things in the tree knot. When no one claims the twine, Scout says, "From then on, we considered everything we found in the knot-hole our property."
The next item they find is the soap dolls.
Jem and I were trotting in our orbit one mild October afternoon when our knot-hole stopped us again. Something white was inside this time. Jem let me do the honors: I pulled out two small images carved in soap. One was the figure of a boy, the other wore a crude dress. Before I remembered that there was no such thing as hoo-dooing [voodoo], I shrieked and threw them down. Jem snatched them up.
“What’s the matter with you?” he yelled. He rubbed the figures free of red dust. “These are good,” he said. “I’ve never seen any these good.” He held them down to me. They were almost perfect miniatures of two children. The boy had on shorts, and a shock of soapy hair fell to his eyebrows. I looked up at Jem. A point of straight brown hair kicked downwards from his part. I had never noticed it before. Jem looked from the girl-doll to me. The girl-doll wore bangs. So did I.
Two things are clear from this particular gift: Boo Radley's gifts have been intended specifically for Jem and Scout and he has been watching them (and probably all of their shenanigans) enough to be able to reproduce their likenesses in these soap carvings. While there is no explicit explanation for Boo Radley's placing these items in the tree, it is evident that he is doing what he can to befriend Jem and Scout, perhaps even repaying them for being so entertaining.
Several more gifts appear, but one day the children discover the hole has been filled with cement by Nathan Radley.