It's a double whammy again!
First, try this tricky tongue twister. Say it as many times as you can (at least three times).
The sick sheik's sixth sheep's sick.
Now, try this even trickier tongue twister. According to the Guiness Book of records it's the most difficult tongue twister in the world. (To minimise the risk of injury, I'd just say it once, if I were you.)
The sixth sick sheik's sixth sheep's sick.
You can listen to them here, and if you have an account with Voice Thread you can leave your own recording or comments (don't worry it's free to leave a message).
More Tongue Twisters