Will it sink or will it float? Zoe wants to help Rocco the rock float, but Rocco is too heavy. Leela sees this as an opportunity for a group experiment, so she, Elmo, and Zoe put their heads together to invent the perfect boat to keep Rocco afloat. Special guest star Craig Ferguson explains what the word experiment means. Plus, the fairy friends are building a giant tower over at Abby's Flying Fairy School, and Bert and Ernie are cavemen in Bert and Ernie's Great Adventures. Murray experiments with cars and ramps, and over in Elmo's World, it's all about hands.