Can't do it

A famous magician had a thundering finish to his act.
He would fill a large boul with shit and proceed to slurp it noisily, to the amazement of his audience.

One night he had just begun the wow finish of his act when he stopped in his tracks.
“Go ahead,” said the stage manager. “Eat the shit, eat the shit!”

“I just can’t do it”, said the magician. “There’s a hair in it!”