Sploid:

At some point in your life you’ve almost certainly marveled at the classic drinking bird toy, and probably lost a few brain cells trying to figure out how it works. Don’t be ashamed if you never successfully unravelled the science, though, as engineerguy Bill Hammack explains, even Einstein apparently couldn’t crack it.

So how does it work? Einstein refused to disassemble the toy to reveal its secrets, but Hammack did, and the science and engineering that power it are utterly fascinating. Invented in 1946 by a Bell Labs scientists named Miles V. Sullivan, the drinking bird’s most interesting illusion isn’t its thirst, it’s the liquid inside.

Holy crap. This is brilliant. I often wondered as a kid why this happened. I haven’t seen one of these drinking birds in years.