Cat in the Hat Knows A Lot About That! - episode: 304
Nick and Sally are having a sleepover in the treehouse and Nick is startled by a shadow. The Cat explains that shadows aren't scary if you know what they are. He takes them to Silhouette Valley where they learn that shadows are made by blocking light and the position of the light can make shadows grow or shrink. Nick unintentionally loses Sally's bouncy ball. They go to Ballaballo and learn how different balls are made of different materials, which help them move in different ways.