Matteo 8:32

And He said unto them, Go. And when they were come out, they went into the herd of swine; and, behold, the whole herd of swine ran violently down a steep place into the sea, and perished in the waters.

In the same neighborhood, at some distance from the place where Jesus was standing, and yet within sight. A great herd of swine, animals that were unclean to the Jewish people, by the Old Testament Law. It was a neighborhood in which the heathen element of the population predominated, where the strictness of the Law was no longer recognized. Knowing that their power over these two men was at an end, the evil spirits begged to be permitted to wreak their fiendishness on the swine, always with the purpose of destruction in mind.

And having obtained the permission, their advent into the herd deprived the animals of even the instinct of self-preservation. Rushing down the declivity, they were drowned in the sea. The devil is a murderer from the beginning. If God hinders his work of destruction against human beings, he kills dumb animals. But he can do nothing without the permission of God. And this permission is granted sometimes in order to carry out some punishment of God.