Jamieson, Fausset and Brown on Mark 5:12

12. And all the devils besought him, saying--"if thou cast us out" (Mt 8:31).

Send us into the swine, that we may enter into them--Had they spoken out all their mind, perhaps this would have been it: "If we must quit our hold of this man, suffer us to continue our work of mischief in another form, that by entering these swine, and thus destroying the people's property, we may steel their hearts against Thee!"