Food that turns from liquid to solid?

My friend Nick Bilton has a good question. If you have an answer, please post in the comments.

Q. What natural food, other than eggs, turns from a liquid to solid, when heated?



The question only pertains to a natural food, no additional things added (so no water and sugar). Just a simple, single food. I've asked so many people and no one has an answer. I even asked friends at The Food Network and nothing. Joel's been trying to find out too and he's lost. Got any insight into this or know anyone that might? A lot of people have said blood, but that just evaporates and then changes, it doesn't actually change consistency.