Thumb Sucker?

We've caught AJ doing this a few times the past couple of weeks. There doesn't seem to be any rhymy or reason to it, so maybe she just likes to chew on her thumb or feel her teeth every now and again? Mommy just had to grab a picture of it since both of us never got addicited to a pacifier or our thumbs...maybe AJ is just starting the thumb thing. Mommy says she already has a few crooked teeth and will need braces, but we don't need to make it worse.