Book excerpt: 99 Tortuous, Tricky, Tough Tongue Twisters to keep you amused for hours. Challenge yourself and your friends to see who really is the tongue twister champion. Includes the 'World's Hardest Tongue Twister', as researched by psychologists at MIT. Not only are you guaranteed fun and laughter, but tongue twisters have been proven to improve English pronunciation skills too, for both native speakers and foreign language students.