Work your brain! Between 2 and 3 pounds of wonder, it controls everything we say, do or think, who we are and what we care about, the way we walk or laugh or figure out things, what we like and the talents we possess, how we see and talk and run and jump and process our food. The brain uses 20 percent of our body's oxygen and 20 percent of its blood. Somewhere within its protein, fat, 100,000 miles of blood vessels and 100 billion nerve cells, it helps us remember where we put our gym shoes. Change our temperature so we don't die because of the heat or cold. Speed us up or slow us down