As babies gain the skills to open and close their fingers, they often delight in dropping and throwing small objects. They might fling toys out of their playpens or off their highchairs, repeating the process over and over again for family and friends.
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.