A study by Current Biology suggests that newborn babies have minimal limitations when it comes to replicating the faces and gestures that they see. This is very different than what we used to believe: that many baby expressions were the cause of biological stuff happening in the body, like smiles forming from gas bubbles.
Although some of these scientific reasons for expressions still hold true, a baby's expressions may actually be a form of true mimicking of what he sees. So, a less-than-pleasing expression could be a mirror image of Mom making a face at Dad. Even in the first 9 weeks of life, imitation it totally possible for a newborn.
Some are adorable, some are funny, and others make us want to know what is going on inside baby's head to get THAT face.
Much like older children and adults, babies can make faces that mirror what they're thinking. So, that look of complete fascination may suggest that she is studying the world around her and forming opinions. In other words, baby wants to learn more!
Babies can also emote anger through more than just a tantrum. Their faces can say it all, with pointed brows and overly-pouted mouths. And complete happiness is possibly the cutest expression for parents to see on their babies. Bright eyes, adorable smiles, complete with coos and giggles.
Whatever the expression, rest assured that a baby is truly trying to express his thoughts, and not simply trying to amuse us (although, that works too!) through exaggerated faces.