How Does the Drinking Bird Work?

Don't even try to tell us that you haven't wondered about this one.

The secret to the bird is not, in fact, patenting and selling such a useless invention. (That distinction, I believe, is held by the person who invented pet rocks. Kudos, whoever you are.) It is choosing the right liquid to fill the bird with. The commercial birds are filled with methylene chloride, but it could be any liquid that turns to vapor at low temperatures.

After that, all it takes is measuring the right proportions of the two bulbs and the tube that separates them. The tube should extend almost entirely into the lower bulb.