Welcome to the wonderful world of tongue twisters...
A tongue-twister is a phrase that is deliberately designed to be difficult to articulate properly, and can be used as a type of spoken word game.
While some tongue-twisters produce results which are humorous - or humorously vulgar - when they are mispronounced, others simply rely on the embarrasssment of the speaker for their amusement value.
Tongue-twisters may rely on rapid alternation between similar but distinct phonemes, unfamiliar constructs, or other features of a spoken language in order to be difficult to articulate.
Many tongue-twisters use a combination of alliteration and rhyme. They have two or more sequences of sounds that require repositioning the tongue between syllables, then the same sounds are repeated in a different sequence.
Some tongue-twisters take the form of words or short phrases which become tongue-twisters when repeated rapidly.