The Fill 'N' Spill Action Cups include four interchangeable and brightly colored bath cups to create different effects in the tub. One cup leaks water, another has a spinning propeller, and the third features a peek-a-boo friend who likes to float when filled with water. The cup holder attaches to the tub for playing, stacking, and storage. This bath toy promotes STEM by introducing children to the cause and effect process.