A well-intentioned teacher was giving a lesson on blood circulation. Trying to make the matter clear, she explains, "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," responds the class.
"Then why is it that while I am standing upright the blood doesn't run into my feet?"
The answer then comes from the back of the class, "Cause your feet ain't empty."
