A daft rhyme about shaving a pig for a wig, answered with a very precise count of hairs. The absurdity is the whole point, and children tend to ask for it again just for the pig. Over in four lines.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Barber, barber, shave a pig.
How many hairs will make a wig?
Four and twenty; that's enough.
Give the barber a pinch of snuff.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition