"A person in charge of a tame animal, mansuetae naturae, is not liable for damage caused by the animal which is foreign to its' nature."

So if your cow knocks somebody down and tramples them, you can avoid paying compensation if you can prove that the cow deliberately and intentionally attacked the person with intent ot cause harm.

If, on the other hand, it is proved that the occurence was accidental and the cow had no aggressive intentions, you have to pay.

Makes perfect sense, doesn't it?