If I set a dog *on* someone, I make the dog attack that person. If I set Bob *against* Sally, I make Bob dislike Sally. You set a dog on me! I'm bleeding, and I have to go to the hospital! I asked you to babysit my dog, but somehow you set him against me. My dog doesn't love me anymore, and he runs away when I call his name! What did you do?! In America, we're more likely to "sic" a dog on someone than "set" a dog on them. He sicced his dog on me! It bit off my finger!