A tongue-twister is a phrase that is designed to be difficult to speak properly.
Usually tongue-twisters rely on similar but distinct phonemes (e.g. s and sh), unfamiliar constructs, or other features of a language.
Tongue Twisters, amazing fun with friends and family
Tongue Twister of the Day
I saw a saw in Arkansas, that would outsaw any saw I ever saw, and if you got a saw that will outsaw the saw I saw in Arkansas let me see your saw.