You always hear of babies being referred to as a Little Bundle of Joy. What they never say (out loud) is that your baby can be a bundle of... well, a lot of things. And whatever they're a bundle of can change in a matter of mere seconds! Once they're old enough they can, and will, cycle through emotions faster than Charlie Sheen.
Such as but not limited to:
While joy is undoubtedly a fan favorite, there is something remarkably cute about an angry baby. They have very few methods of communicating their rage (or anything) at first, so they just scowl and growl at you like a ferocious puppy. An instant later they're smiling and laughing again. Winning!