What makes popcorn pop?

Question: What makes popcorn pop?
- Keywords:
  food,
  popcorn
Asked by issi759 to Alessandro, Angela, Claudia, Marina, Phil on 13 Mar 2013.
- Alessandro Guazzi answered on 13 Mar 2013:
  
  There’s a little bit of water inside the corn kernels, which when it boils turns to steam, expands, and causes the popcorn to explode and turn inside out!
  http://www.nasa.gov/audience/forkids/home/popcorn.html
- Claudia Krehl answered on 13 Mar 2013:
  
  It’s great fun to make popcorn the old fashioned way at home and watch them pop in your pan!

Question: What makes popcorn pop?