What happens when you put a banana into liquid nitrogen? Well... lets see:
(this definitely provided a nice distraction from the afternoon laboratory session 
)
OK, so that's cool.. but why does freezing a banana make it so brittle? Well... bananas have a large water content. As the banana is frozen this causes millions of tiny ice crystals to form. These form in many different spots and aren't very well aligned (this is called a grain boundary). The presence of many weak boundaries makes it very easy to shatter the banana. A good analogue is to think of ice. A big block of solid ice (so one large crystal) is much easier to break up than a bag of ice cubes that are all stuck together (if you don't believe me go give it a go!). Also, the freezing causes damage to the cell walls of the banana, making them much weaker than normal (and thus a reason why films likes Demolition Man will never happen... unless we make some massive progress in science).
