As of October 2009, your baby could show you their different expressions, making them look more realistic. Some of those expressions are: Tired, sad, angry/mad, and happy. Your baby will preform these expressions when they feel it is needed. Sometimes the expressions will 'tell' you what your baby wants or needs.
The most common expression your baby will make is the happy or content face, which means you are taking excellent care of your baby, and they are having fun. If you are not taking good care of your baby they will look angry; in order to take good care of your baby you need to keep them well and healthy.
When Expressions Occur[]
The Tired Expression will appear: When it is bedtime, 20:00 or later. When your baby gets bored of a toy or book.
The Happy Expression will appear: When you are taking good care of your baby, playing, cleaning and feeding them.
The Sad Expression will appear: When your baby has lost its snuggly, or when they wake up in the middle of the night.
The Angry Expression will appear: When you are not taking good care of your baby by keeping them in poor condition, or if one of their Wellness bars drop to 0%.
The 'Upside-Down Triangle' Expression will appear: Most likely, when they ask for the potty, or just went in their diaper.
Expressions
Ow's forum post on expressions