A movie about a man and a dog dancing in the square dance.

The motor system of mammals consists of bones, osseointegration and skeletal muscle. Changes in the position of bones produce motion, but bones themselves cannot produce motion. The movement of skeleton depends on the traction of skeletal muscle, which has the characteristics of stimulated contraction. When skeletal muscles contract under the stimulation of nerves, it will affect the movement of bones around joints, so the body will move.

Learning behavior is gradually established through life experience and "learning" during the growth of animals after birth. Dogs can also do some actions with the rhythm of music, which is a learning behavior.

So, the answer is: joints; ? Skeletal muscle; Nervous system; Study the day after tomorrow.