What happens to dampen the children's enthusiasm for their game in chapter 4?

One day Atticus catches them playing the game and asks them if it has anything to do with the Radley family. They deny it, and Atticus replies, "I hope it doesn't." Atticus's sternness forces them to stop playing, and Scout is relieved because she's worried for another reason: she thought she heard the sound of someone laughing inside the Radley house when her tire rolled into their yard.