A teacher was giving a lesson on the circulation of the blood.
Trying to make the matter clearer, he said:
“Now, students, if I stood on my head the blood, as
you know, would run into it, and I
should turn red in the face.”
“Yes, sir,” the boys 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, “It’s because
yer feet ain’t empty.”