A Kids Reply

A teacher was giving a lesson to her young students on the circulation of blood in their bodies.
Trying to explain the lesson clearer, she told her class if I stood on my head, the blood as you know would run into my head and I would turn red in the face.
"Yes," the class said.
"Then why is it that while I am standing upright position the blood doesn't run into my feet and make them turn red?"
A young boy shouted, "Because your feet ain't empty."