Hen moving bottom up and down while sitting.

[JonnyMoore]

Our hen is consistently laying eggs every other day, or sooner. I've often find her sitting down low in her favorite spots, thrusting her pelvis up and down in rhythm.

Is she..
A) preparing to lay?
B) Moving the egg around in side to better (more evenly) create the shell?
C) Just being a horny little hen
D) Something else?

 

[aart]

How much movement is there?
The rear end will move some as they breathe.
A video would really help here @JonnyMoore .
Upload vid to youtube, or similar platform, then link here.