According to the Guiness book of records this is the hardest tongue twister in the English language.
The sixth sick sheik's sixth sheep's sick.
I don't have much trouble with tongue twisters myself. I seem to be able to say them all quickly, over and over again.
Red lorry yellow lorry is another that seems to fox a lot of people.
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Old aunts used to come up to me at weddings, poking me in the ribs, cackling and telling me
'You'll be next.' They stopped when I started doing the same to them at funerals.