Is this head bobbing?

[Baconosaur]

Recently I caught my beardie basking with his beard puffed out. It didn't have any coloration to it, and as I watched, it began to jerk it's head up at sudden, seemingly random intervals. I haven't seen it do it since, but I was wondering what this might mean. Is this some sort of intimidation at a reflection, or a mating dance? Or maybe something completely different?

 

[xp29]

Both
They use stomps and bobs to intimidate other dragons and also to try and dominate/impress a mate.
Reflections in the glass can trigger them