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
A tree toad loved a she-toad Who lived up in a tree. He was a two-toed tree toad But a three-toed toad was she. The two-toed tree toad tried to win The three-toed she-toad's heart, For the two-toed tree toad loved the ground That the three-toed tree toad trod. But the two-toed tree toad tried in vain. He couldn't please her whim. From her tree toad bower With her three-toed power The she-toad vetoed him.