Drinking Bird (4C31.30)
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Commercial novelty item. Dip the bird's beak into a beaker of water, then let it go. Evaporation of the water from the wet beak cools the beak, lowering the vapor pressure of the liquid inside and drawing it up into the head. That overbalances the bird and it tips into the water for a "drink." In that position, the liquid inside flows back into the lower bulb, which rights the bird and starts the cycle over. Note: This is not very visable for a large class without using a camera.