Simplify the following text for a Grade 8 native English-speaking person.
Original: As defined in the Oxford English Dictionary , the `` bridle '' includes both the headstall that holds a bit that goes in the mouth of a horse , and the reins that are attached to the bit .
Simplified: The bridle includes the headstall ( that goes around the horse 's head ) and holds a bit that goes in the mouth of a horse , and also the reins that are joined to the bit .