Most of us don't give more thought to pancakes than how to wolf them down. But some French computer scientists [Laurent Bulteau, Guillaume Fertin and Irena Rusu] had nothing better to do than study them for some leisurely analysis on the sorting a permutation using prefix reversal algorithm. We can thank them for proving the problem isn't just hard, it's NP-Hard. In a nutshell, you're supposed to sort a pancake stack into size order where your only operation is to insert a spatula and flip the entire upper pile over repeatedly. You can explode your brain with their mathematics reading the published paper (pdf).