Babies begin voicing their emotions and desires frequently at 5 or 6 months, laughing to show pleasure and crying when they want a different toy or a change in activity. Babies are learning to communicate about things other than their immediate needs.
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.