You might know that a googol -- the digit 1 followed by 100 zeroes -- is a very large number indeed. You might even know that a googolplex -- a 1 followed by a googol of zeros -- is an even bigger number. But this video helps explain why it's such an insane concept to get your head round.
The video's ably presented by Matt Parker and the brilliant Helen Arney, who make the whole thing light, breezy and really quite funny. It's well worth watching -- although don't blame us if it makes your brain hurt just a little bit. [Numberphile]