Originally Posted by rookie
I tried them both in a Dr. Cooks bitless bridle. The mare was confused because it uses poll pressure instead of mouth
Agree with all of the above & I suspect there's more to it. But horses can indeed just 'hate the bit' without physical problems, due to prior or current handling/training with it. And it is generally easier to hurt a horse with a bit than with a halter(that doesn't apply to all bitless, such as mechanical ones), so I start all my horses - and novice riders - in a halter, and 'retrain' horses in a halter, not moving/returning to a bit until they're yielding very well in a halter.
Oh yeah, I quoted the above from Rookie because this is also relevant - horses don't generalise that well, so if bridle cues feel different, they need to be *taught*, not just assumed It Is Known. Different bitless bridles feel different too. I always give the horse an on ground 'refresher' lesson or few before getting onto their back in different equipment, and would start riding in a controlled environment, so you can *ask* the horse to respond to it without having to *need* them to instantly.