Running On Empty

    An Army instructor was giving a lesson on survival that involved some basic understanding of the circulation of the blood.

    "To make the matter clearer," said he, "Now, men, 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 reply came.

    "Then why is it that while I am standing upright in the ordinary position the blood doesn't run into my feet?"

    A brave soul offered the response, "'Cause yer feet ain't empty, Sarge."