Trap a peep under a bell jar and suck out all the air with a vacuum pump. What do you think happens to the peep? (Hint: It doesn't end well for our marshmallowy friend.)
Photo Credit: Kate Ter Haar CC BY 2.0
Bad Astronomer-cum-peep-slayer Phil Plait recently had a chance to answer this question at the Texas A&M University Physics and Engineering Festival. Fortunately for all of us, he recorded the results for posterity:
Because the Peep is soft, the material around the holes gets pushed by the air and expands as well, inflating the Peep overall. The tension in the material itself provides a force that keeps the air from expanding into the jar, so at some point the expansion stops when the forces balance.
However, that material is made of sugar molecules all stuck together in a crystalline state. When the Peep expands, the crystal structure is partially broken, and it stays expanded only because the air pressure inside the bubbles is holding it up, balanced by the tension in the sugar. Once the air is let back into the bell jar the air inside the bubbles contracts again, and the material collapses.
Poor little peep never stood a chance.
See also: 100 Ways to Kill a Peep.