Why do rabbits bumps your hand with their head when you put hand in the cage?

It has been my experience with my pet bunny that the nudging means he/she wants to be petted or for you to continue with the petting if you stopped. The nipping is when your pet is telling you that he/she has had enough. The nipping could also be playful jesters and your pet may misjudge the distance with his teeth; this is not intentional behavior.