Come for the science, stay for the explosions. Watch Plymouth University professor Roy Lowry* demonstrate what happens when you try to contain liquid nitrogen while it's returning to its gaseous state. (The impatient among you can skip to 3:15.)
*Fun (though, given the nature of this video, perhaps not entirely surprising) fact: In 2006, Dr. Roy "Rocket Man" Lowry claimed the Guinness World Record for "most rockets launched simultaneously." How many rockets, you ask? 56,645:
According to the BBC, Lowry's feat outstripped the previous record by 17,439 rockets and required a whopping 250 kilograms of gun powder. Not to pooh-pooh on the ping pong balls, but damn.