What do you suppose makes the muscles of the leg contract when the brain is asleep and does not know that the foot is being tickled?
And here is another curious fact.

When you were coming to school this morning you did not have to think about every step you took.
Perhaps you were talking or looking over your lessons; but your legs walked right along all the time, and without your thinking about them.
Can you tell how?
~22.~ It would be too much trouble for the large brain to stop to think every time we step, and the little brain has work enough to do in taking care of the heart and lungs and other organs, without keeping watch of the feet when we are asleep, so as to pull them up if some mischievous person tickles them.

So Nature puts a few nerve cells in the spinal cord which can do a certain easy kind of thinking.

When we do things over and over a great many times, these cells, after a time, learn to do them without the help of the large brain.

This is the way a piano-player becomes so expert.