Most babies around 12 months 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. Now capable of poking with the index finger, they explore holes by poking them. Babies don't know where it's safe to poke their fingers, so dangerous places like electrical outlets need to be covered.
References
- 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.