This is a video from the Crazy Russian Hacker demonstrating what happens when you stick coins in a block of dry ice. What happens? They shiver. WHY do they shiver? BECAUSE THEY'RE COLD, WHY ELSE WOULD THEY. Just kidding, because science. Or is it magic? Allegedly it's science but I'm still not sold yet.
The cause of the motion is that when the coin comes into contact with the dry ice, it heats the ice above its freezing point, and the frozen carbon dioxide sublimates back to a gas. That collection of gas pushes on the coin as it escapes, causing the coin to move and make different points of contact with the ice.
You stick my ass in a block of dry ice and I guarantee I'd shiver too. That reminds me -- my mom told me when she was in college the student government held a series of prize contests including one to one to see who could sit on a block of dry ice the longest and all six participants had to get parts of their buttcheeks removed and skin grafted, true story. So, if you ever get on the bus or subway and the only available seat is made out of dry ice, what are you gonna do? "Wonder why there's a seat made out of dry ice?" No -- you are going to STAND. You are going to stand and pass your phone around and make everyone take turns reading Geekologie articles out loud.
Keep going for the whole video.
Thanks to Lydia, who did the same thing with a dollar bill with much less interesting results. Plus I took the dollar when she wasn't looking.