The part of the tack (harness) that fits in the mouth of a horse is the bit.
There is a long list to how horses communicate. Horses use their ears, mouth, they nudge you and sometimes head-butt you and many more ways.
It is a possibly, but there are no reported cases of it in horses.
A plain snaffle or a happy mouth.
fod
Their mouth....
A horses bars are the toothless spaces in it's mouth, where the bit is placed.
A bit is metal bar that is on the bottom of the bridle. This fits inside the horses mouth, behind the teeth, where there is a gap.
The bit
it is called a bit
Chewing Licking Swallowing Cleaning its mouth area Greeting other horses Prehensilely to handle certain objects
hold it near the horses mouth but don't bang his/her teeth
you got it straight from the source