By now, you may have already told your baby that the telephone is not a toy, or that rattles are not for throwing, or that her sister's hair is not for pulling. At this age your baby may begin testing your authority by refusing to follow your simple directions. She's not really being disobedient or willful — just curious.
Keep in mind that she also simply can't remember things you tell her for more than a couple of seconds at a time. The best tactic is to use a simple "no" and then distract her.
Your baby's beginning to understand how objects relate to one another in three-dimensional space. She may be able to sort toys, grouping smaller items by size. Babies instinctively combine objects by stacking them and, as they get older, trying to fit them inside one another.
If your baby admires her reflection in a mirror and you suddenly appear behind her image, she's likely to turn and look for you instead of believing that you're in the mirror itself.
A simple game of peek-a-boo might be absolutely fascinating to your baby. That's because she's starting to understand object permanence (that an object she can't see can still exist) and loves games in which people or things appear and disappear.
Your baby can now straighten her back and twist her trunk as she sits. This ability enables her to sit for longer periods of play.