Babies as young as months) learned that their own kicking moves a mobile; and they retained that learning without later practice for as long as month(s).

Babies that are three months old are capable of learning this, and they retain the knowledge for one month if it is not reinforced. By this point, an infant's vision is good enough that they can see the mobile above them, and not just their mother's face, which was the range of their vision at birth. Their cognitive processes are also developed enough to connect their action to the mobile's movement.

The one that most represents the earths mantle would be the skin since the mantle is the upper part of the earths depths which is just like the skin of an apple.