Ateacher was giving a lesson on the circulation of the blood. Trying to make the matter clearer, she said, ´Now, class, if I stood on my head, the blood, as you know, would run into it, and I would turn red in the face.´
´Yes,´ the class said.
´Then why is it that while I am standing upright in the ordinary position the blood doesn´t run into my feet?´
A little fellow shouted, ´Cause your feet ain´t empty.´