The bit is also called the armature. In feudal times in China, all warhorses had to bite an iron bar with a belt, and the other end of the iron bar was tied to the REINS in the master's hand.
Whenever the horse wants to move, the owner will say something similar to "ride", "sigh", "talk", "tie" and so on, but these words are not fully understood by the horse, in addition to verbal commands, but also with other actions.
For example, when the word "drive" is said, the knight must press the horse's belly and then strike the horse's buttocks with the whip in his hand. Only words and body work together to make the warhorse understand the urgency of the command. This is somewhat similar to the collar on the nose of the cow, because people are generally not as strong as the cow, so you need to use some tools to control.
Of course, the word "sigh" does not mean that the horse will stop, but to pull back the rope in the hand, let the iron in the horse's mouth move, stimulate the horse's jaw, let the horse make a struggle action, and then will stop.
Another function of the bit is to prevent the horse from eating while it is on the move. Some people even make a set of REINS to put around the horse's mouth, which serve the same function. You may not have seen a bridle, but you all know that it's like a mask that prevents cows, horses, and other animals from eating while they're working.