Try seeing how good you are at reading out some of these tongue twisters. Better still, record your efforts and send them in to us. We'll post them up on this web site so you can show off to all your friends how good you are!
Here's one recorded by Lixue...
si shi si, shi shi shi, shi si shi shi si, si shi shi si shi.
Which means something like: 'four is four, ten is ten, fourteen is fourteen, forty is forty'