Three American Indian women in the wild west are about to give birth.
One is lying on a buffalo skin; one is lying on a moose skin; and one is lying on a hippopotamus skin.
The first woman gives birth to a boy.
The second gives birth to a girl.
And the third gives birth to a boy and a girl.
And this proves . . . the squaw of the hide of the hippopotamus is equal to the sum of the squaws of the other two hides.