Aww, poor Tinkerbell! I hope she feels a lot better now.
Yoda can get like that too and sulk after he growls for attention and doesn't get it. I think part of it is that while we have other things to entertain us (Internet, TV, music, and other people), their whole lives revolve around us (and perhaps any furry brothers and sisters). So when they don't get the attention from us, they can get sad about it, since their lives revolve around us ONLY. If that makes any sense...