If you're familiar with the drinking bird toy, you know it as a cheesy knickknack that's adorned office desktops for decades. But anyone with a background in thermodynamics knows that the novelty item deserves more credit. In his video spotted by Sploid, Bill Hammack—a.k.a. engineerguy—explains the impressive science at work every time the toy takes a sip.
To pull off its famous trick, a drinking bird toy must contain a special chemical compound called methylene chloride. When stored inside the toy it looks like colored water, but its properties are unique: It can transition easily from a liquid to a gas by essentially boiling at room temperature. Evaporated methylene chloride fills the bird's head while liquid methylene chloride fills the base of its body. Pressure differences caused by the condensing gas in the head encourage the liquid in the base to rise to the top of the toy, shifting the weight so its upper half topples forward into the glass in front of it. The liquid methylene chloride drains out in this new position and the balance of gas and liquid is restored. As long as the bird has enough room-temperature water to drink, the water will cool the methylene chloride vapor and start the whole process over again.
The result is a seemingly simple toy whose principles were actually complicated enough to baffle Albert Einstein. You can watch Hammack give a more detailed explanation of the science at work in the video below.