At the beginning of Chapter 4, Scout finds chewing gum in the knothole of the Radley tree. Later on, she and Jem discover a pair of Indian-head pennies in the same spot. These two events foreshadow Scout's revelation that Boo Radley is still alive and lives inside the house. As the chapter continues, Jem rolls Scout in a tire down the street, and she accidentally crashes into the Radley porch. Scout gets up in a daze and Jem runs inside the Radley fence to grab the tire. After the children drink their lemonade and take a break from playing, Jem says they're going to a play a new game called "Boo Radley." At first, Scout decides she's not going to play and mentions that Boo can get out at night and harm them. Jem claims that Boo Radley has been dead for years and was stuffed up a chimney. Scout says,
"I was fairly sure Boo Radley was inside that house, but I couldn't prove it, and felt it best to keep my mouth shut or I would be accused of believing in Hot Steams, phenomena I was immune to in the daytime." (Lee 51)
Scout decides to play, and the children act out a "melancholy drama" they name "One Man's Family." One day, Atticus sees the children playing and asks Jem if it has anything to do with the Radleys. Jem says it doesn't, then tells Scout and Dill that they should continue to play. Scout comments that Atticus' arrival is the second reason she wanted to quit the game. She says,
"The first reason happened the day I rolled into the Radley front yard. Through all the head-shaking, quelling of nausea and Jem-yelling, I had heard another sound, so low I could not have heard it from the side-walk. Someone inside the house was laughing." (Lee 54)
The last sentence of Chapter 4 is when Scout reveals why she feels certain that someone is inside the house. Scout believes that Boo Radley was the person she heard laughing. Not only does Boo Radley secretly give the children gifts at the beginning of the chapter, but he also laughs at Scout when she crashes into the house. His friendly, light-hearted actions suggest that he is not the "malevolent phantom" that the children think he is.