"Chafe the bit" is a phrase used to describe when a horse becomes anxious or restless due to the pressure of the bit in its mouth. However, there are many synonyms for this phrase that can be used to describe different degrees of discomfort or unease in a horse. Some examples include "bite the bit," "paw the ground," "toss the head," "rear up," "run away," "spook," or "balk." Each of these expressions captures a unique aspect of a horse's reaction to the bit, and can be useful for horse owners, trainers, or riders who want to communicate effectively with their equine partner.