is like the courtyard of the injured party, i.e., it is not a separate domain from the place in which the animal is eating. As if the mouth of the animal were to be considered like the courtyard of the one responsible for the damage, let the owner of the dog say to the injured party: What is your bread doing in my dog’s mouth? The dog’s mouth is my domain, and I am not liable for damage classified as Eating done to your property in my domain.
דאיבעיא להו: פי פרה – כחצר הניזק דמי, או כחצר המזיק דמי?
The Talmud notes: The need for this type of inference arises from the fact that a dilemma was raised before the rabbis: Is the mouth of a cow like the courtyard of the injured party, or is it like the courtyard of the one responsible for the damage, i.e., the owner of the cow?
The Talmud asks: But if you say that the mouth of the cow is like the courtyard of the one responsible for the damage, how can you find a case of damage classified as Eating for which God holds the owner of the animal liable? The halakha is that one must pay for damage classified as Eating only if it occurred on the property of the injured party. If the mouth of an animal is deemed the domain of the animal’s owner, damage caused by an animal eating would always take place in the domain of the animal’s owner and he would therefore be exempt from liability in every case.