Parakeet bahavior questions - What's it mean?

[Parakeet]

I have 2 males (about 1 year old each) budgies in the same cage together, and a lot of the time, when I'm playing with them inside their cage, they sorta bite my finger like it's some sort of millet spray. I was just wondering, what does this behavior mean? And also, sometimes, one of them slightly raises the feathers above their beak and its pupil gets smaller (like what happens to human eyes when exposed to too much sun). What does this mean?

[zazanomore]

My budgies do the same thing. If it's not hard aggressive biting, then it's just exploring and having fun.

As for the eyes, they do this when they are excited. Completely normal, nothing to worry about

[liz]

My kids preen me. Could that be what they are doing?