S2·E22 Keep the Beat

Nick and Sally have been running around the backyard and now their chests are thumping along. The Cat explains that this is their hearts booming. A visit to Dr. Giggles, he will answer that question: by shrinking down super small, they follow Dr. Giggles' directions to follow the path that blood takes, learning about how the heart is a pump. They watch Thing 2's heart beat faster when he runs, and slow down when he stops. With all this running around, their bodies are now making another sound: rumbling tummies.