Few scientific presentations really make one hungry (or thirsty), but today’s demonstration of the ‘hot chocolate effect’ did just that.

Tap a spoon on the inside bottom of a mug of hot chocolate, and you’ll hear a rising pitch that keeps rising as you keep tapping. It’s a fascinating physics experiment that can be done apres-ski. But don’t limit yourself to just hot chocolate, says Bradley Carroll of Weber State University in Utah. It works for other beverages, including instant coffee and even cold beer.

It all has to do with tiny bubbles in the liquid. They slow down the speed of sound, so the pitch you hear is lower at first. As the bubbles rise to the surface and break, the speed of sound in the liquid rises, so the pitch rises in tone.

Try it out for yourself. Don’t take my word for it.