Meaning of horse putting head over shoulder

[little_critter]

My mare uses it as a “don’t do that” sign. Eg if I’m pulling her mane or something else she finds uncomfortable, she will put her head on my shoulder to stop me. There is no aggression, just like a mother putting her hand on a child’s hand to shop him picking a scab or similar.
(I no longer pull manes, if they need to go shorter I use scissors and feather the cut edge as best I can. )