Mouthing is a term used to describe the action of a horse using its teeth and lips in order to manipulate objects such as bits, ropes, and other items. It is an important part of training horses, as it helps them learn how to respond correctly when asked by the rider. Mouthing teaches horses not only how to accept something in their mouth but also to understand pressure from the reins or bit. It can be done with either light contact between the bit and tongue or more firm contact for teaching more advanced movements like lateral flexion. The goal should always be that mouthing causes no pain for the horse; if he shows signs of discomfort then you need to adjust your technique so that he learns without feeling any kind of displeasure.