The poll is a name of the part of an animal's head, alternatively referencing a point immediately behind or right between the ears.
Specifically, the "poll" refers to the occipital protrusion at the back of the skull.
The area at the joint has a slight depression, and is a sensitive location.
Thus, because the crownpiece of a bridle passes over the poll joint, a rider can indirectly exert pressure on the horse's poll by means of the reins, bit, and bridle.
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