Thank You Dan for this post, My babies do bite me at times when they play. I am also learning too that when they do Beak it's because that's there 3rd foot. When they twins are playing and don't want to go back to there cage I have my kids try and get them down, well when they do bite them my kids are afraid. I tell them don't be afraid and then I go and get them! Yeah they may do the nipping thing but it dosen't hurt me and I don't back down either.
So I do believe that they use there beaks to either defend themselves from bad things when they need to BUT I also believe that they use there beaks as a third foot as well.