Strange robin behaviour (1 Viewer)

I have just witnessed something I've not seen before with two robins in the garden. I assume they are a pair and it is a mating behaviour but wondered if it might be some kind of weird posturing between two males.

One of the birds was doing a very, very, slow motion, side to side head movement, with the head down low and forward, eyes fixed on the other bird. Reminded me a bit of a snake in front of a snake charmer, but much slower. Gave me the creeps! A chase ensued for a few minutes and they were gone....

Any ideas anyone?

Given that you witnessed a display (of sorts) followed by a chase, my vote is for courtship behavior. The male may have been trying to attract the female's attention, and when she lost interest he pursued her.