It's a double whammy this time!
First, try this simple, but difficult tongue twister. Say it as many times as you can (at least three times).
She sells seashells on the sea shore.
Now, try this trickier tongue twister. (To minimise the risk of injury, I'd just say it once, if I were you.)
She sells seashells on the seashore.
The shells she sells are surely seashells.
So, if she sells shells on the seashore,
I'm sure she sells seashore shells.
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