How Snaffle Bits Work

Whether you ride English or Western, it's likely that you started out by riding your own horses or by being mounted on a schoolmaster horse while using a snaffle bit. These bits sit comfortably in the horse's mouth in the rear opening between its top and bottom teeth, and can be used with rubber lip guards to prevent pinching its lips.
What is a Snaffle Bit?
A snaffle bit is a common type of horse bit that is gentle on the horse's mouth. Comprised of either a single bar or two to three jointed pieces between large rings on either side, snaffle bits make it easy for riders to communicate with their horse and are commonly used to train young horses and beginner riders.

Even if you don't start out using a snaffle bit, there's a good chance that somewhere along the path of your riding education, you will ride with one. 
 
Knowing how the snaffle bit works is helpful in developing effective rein aids and to avoid being either ineffectual or too hard on your horse's mouth.
Although the basic action of most snaffle bits is the same, it sometimes takes trying a few different bits to find one your horse is comfortable with. Sometimes choosing the right bit, even if you are choosing among snaffles, can take a bit of time.
Snaffle Basics
A snaffle bit has a straight or jointed mouthpiece with rings on each end of the mouthpiece. There are many different types of snaffle bits. The basic structure is the same for all, and the basic action in the horse's mouth is similar, with some subtle modifications. The snaffle bit is regarded as a relatively mild bit. The addition of wire wrapping or other similar mouthpiece variations can make it much harsher.
What Happens When You 'Pull' the Reins