I've wondered about this for a while, so I thought I'd ask - Valo sometimes has this little head twitch thing... it doesn't seem that it's an uncontrolled movement, and he doesn't do it regularly. Usually, it's when he's excited or the TV's on too loud. It's hard to describe - he turns his head rapidly from one side to the other, it's not an upside down movement.
We've a check up next week, and I'm going to ask the vet about it, but it would be great to get your guys' input as well!

I think I would eye any pellets before Kale as a reason. I hope its nothing though!

Sorry Bee I think I kinda blended both of your post!

Peanut can do the same thing, he starts off with quick head movements, then his wings quiver and after that he is left hanging by one foot from the perch. He does this when he is excited to get my attention. By the time he is hanging the entire bird can be shaking and twisting.