Mad at her feet?

We've got a daily routine and Astrid is coming out of her shell. She plays and is getting much better at grasping and holding things. She's (we've just decided to call her she until we can tell what sex she is) got her favorite toys and perches and plays on top of her cage daily. She chatters to herself when she's napping, and occasionally gets startled by something, but generally appears comfortable and likes to hang out with us and on us. Her wings are clipped but she flies down to the floor and explores and climbs. She's got this thing though where she seems to get mad at her feet. She's just perching on top of her cage and curls her talons up and nips at them and screeches like she's frustrated with them. And if your holding her when she does this she sometimes will nip our hands, she seems like she gets really ticked off. It's kind of funny to see, but I was wondering if this is normal? She's too young to have arthritis I think. These little spells don't last long, and they're king of funny to watch. I was just wondering if anyone with experience knew why she does this. :06: