My horse was throwing his head a lot when I cued for certain things, especially turns. I used an eggbutt snaffle, so I thought it might be his teeth. I had the equine dentist out, and his teeth were fine so I switched him to a bitless Little S hack or an indian bosal, depending on what I'm doing. I've also spent more time working on neck reigning and refining leg cues. He's much more attentive and the head tossing has almost completely ceased. I've found that for him, the simpler the bit/bridle, the better. I also do about 10-15 minutes of groundwork prior to riding so he knows it's time to work.