Drippy Cups

It seems like there are two basic style of sippy cups... you know, the ones where the juice/milk/water doesn't come out when it's held upside down. Some work on suction. The baby sucks really hard and the water comes out. When they stop, air is quickly sucked back in to equalize the chamber. The second is more interesting. The entire top is a soft, flexible rubbery plastic. This allows the "straw" to be moved, pressing in on the top and causing juice to come out. Rachel has learned that this cup, when banged on the table upside down causes milk to come out. So, she does this all the time to make milk puddles, which she then delights in splashing in with her hands. What fun.