Could be that the one bobbing its head is a baby and the bird is begging for food from the other bird.
Head-bobbing can mean one of several things, but it does not usually mean aggression. It may be one of the following:It is most commonly courtship behaviour.It can denote excitement, interest and curiosity.
Sounds like your budgie is playing. My budgie head bobs when he is hyper and playing in his cage, when he is practicing "talking" and is cleaning himself at the same time or when there is music on that he likes as if he is dancing to it.
Chinese Water Dragon lizards occasionally express aggressive behaviour toward each other in the form of arm waving, puffing up of the throat, head bobbing and sometimes the chasing is aggressive. Both males and females will perform arm waving, head bobbing, throat puffing, tail flicking and chasing. See the related link for more details.
Depending on your Parakeets color, it's perfectly normal for parakeets to not have blue on it's head...
Velociraptor
snoring , closed eyes, no response, bobbing head.
snoring closed eyes no response bobbing head
It only has 2 legs.
Head bobbing is a completely normal behaviour. They're happy, content, and want attention.
bobbing head eyes closed snoring
I have an informative website on the various 60's & 70's paper mache hockey bobbing head dolls http://www.frontiernet.net/~hknodder/closeups.html http://www.frontiernet.net/~hknodder/Index.shtml
it can grow up to 9 inches from head to tail