The first act in the digestion of food is its prehension (seizure), which is accomplished by the lips and afterwards by the front teeth (incisors = cutters). If the grass, hay, or other food offers resistance to its removal on being caught hold of by the lips, the front teeth will help to detach it by their cutting action, and the upper lip, which is gifted with great mobility, a high degree of sensitiveness, and a fair amount of muscular strength, will be capable of more or less encircling it and of exerting traction on it. The knowledge that the upper lip is very sensitive to pain teaches us that an ordinary twitch should be used only in cases in which the infliction of pain is justified by necessity. Also, the employment of this twitch has the great disadvantage, from a pecuniary point of view, that it is liable to depreciate the animal's value by rendering him difficult to be handled about the head, as for instance, in bridling him. When the food has been detached and is held by the lips, the teeth become separated from each other, and the tongue, aided by the lips, conveys the food to the back of the mouth. Colin has shown by experiment, that a horse is unable to take any solid food into his mouth without the aid of his lips. In cattle, the tongue performs the office of the prehension of food in a manner somewhat similar to that done by the upper lip of a horse.