A tongue twister is a phrase or sentence designed to be difficult to say quickly, usually because it packs similar sounds close together. Try saying “She sells seashells by the seashore” three times fast, and you'll feel your tongue stumbling over itself as the “sh” and “s” sounds blur together.

Tongue twisters work by exploiting how our mouths produce speech. When sounds are too similar and follow too quickly, our brains and tongues get confused. “Peter Piper picked a peck of pickled peppers” forces your lips to keep popping on all those P sounds. “Red lorry, yellow lorry” tangles up the L and R sounds until you're saying something completely mixed up.

People use tongue twisters for fun, but actors and singers also practice them as warm-up exercises to sharpen their pronunciation. Speech therapists sometimes use them to help people improve their articulation. Every language has its own tongue twisters built around whatever sounds trip up speakers of that particular language.