It's really hard to say what may have been going on, Hoofpic, without being there to see it.
Maybe she wasn't feeling like being petted today.
OR, were you perhaps stepping toward her shoulder/head, when this would happen? Maybe she was recalling the training you've done with her on leading and stepping her front end away from you, leaving her butt facing you?
What was the rest of her body language telling you? If her ears were pinned or she was wringing her tail, or threatening to kick by raising a leg, then it was a threatening gesture.
Was she focus on something else? Then maybe she just wasn't interested in you and was checking something else out.
Or maybe it was nothing and she just had enough petting
Who knows. Like I said, I wouldn't worry about it, just see how she is tomorrow.
edit;; I won't put up with dangerous behavior for any reason (not saying that I think what she did was dangerous). A horse can tell me he hurts without trying to make me hurt too. They don't get to put a human's safety in jeopardy just because they don't feel well. Especially a mare in heat. I don't get to go around beating people up when I'm on my period, so I don't let that be an excuse for them either. They can be grumpy, whatever, but I expect them to behave the way I've taught them regardless.
Last edited by enh817; 10-22-2015 at 02:08 AM.