I'm not 100% sure where to post this, so I just picked training.
So, every time I put my horse's bridle on he shakes his head, and won't stop shaking his head until I take it off. It isn't wild or ridiculous head shaking either, it's just very annoying.
I've used the same bridle and bit on him since I bought him over a year ago, and the head shaking is rather new (4 months maybe).
Any thoughts on what might be bugging him?