Isn't it adorable?!!! Even when my little guy pins his eyes out of anger its still so adorable haha. I've noticed mine does the same... He constricts his pupils when I speak to him, when he's really focused on what I'm saying to him. He also does it when he "attacks" his toys, and when he bickers with my other birds. Except when he does it out of anger, the feathers on his neck and head stick straight up LOL

He pins out of excitement when we play peekaboo... and when he talks they constrict as well. I love it too! As far as knowing exactly why they do this.. I wish I knew! I guess it's just one of the cute little ways they show us how they feel
