As they approach 12 months, babies use their improved coordination to thoroughly investigate the objects they encounter, picking them up, banging them on the floor, shaking them, and passing them from one hand to the other. They demonstrate their growing hand and finger skills by placing objects into containers and taking them out again. This is an exciting cognitive exercise as well, because infants this age are just beginning to understand where things go when you can’t see them anymore. Being able to make an object “go away” by putting it into a container and then “come back” by bringing it out is a fun activity they may want to repeat over and over again.
Shelov, S. P. (Editor-in-Chief). (2004.) Caring for Your Baby and Young Child: Birth to Age 5. The American Association of Pediatrics. Revised edition. New York: Bantam Books.