Moses Supposes

Moses supposes his toeses are roses,
But Moses supposes erroneously.
For Moses, he knowses
His toeses aren't roses
As Moses supposes his toeses to be!

A tongue twister

Not much of a tongue twister, since it's terrifically easy to say. The aforenoded poem originated in the classic musical "Singing in the Rain", where it was used by a Hollywood diction coach before being co-opted by the leads for a spontaneous song-and-dance number.