Its weird you say this about the bobbing today my 7 month old male panther did the same thing to me today when I walked past his cage. I think its more of a territorial display to let us know leave me alone biotch!! Reptiles can be conditioned to eat out of your hand without eating your hand and also be picked up but they are still cold blooded very instinctual animals. Im sure someone on here knows the exact answer im just speculating so if someone could chime in on this that would be awesome as I am interested as well.
my male veiled seems to enjoy head bobbing me after I open his cage to fix something, he gets very grumpy when i reach in for his food bowl thinking im going to attack him so he hisses and displays his colors and once he calms down he will head bob, i agree with jaglon53 about it being their way to tell you to stay away from their territory and them, if i dont invade his space he is perfectly fine