Why did my dog bite my dad? It happened 2 times already in about a week. He is never like?

does the dog able to sense if a person is around another dog or animal thats aggressive or smells funny sometimes animals pick up if a person is in a bad mood or if the dog recently was around a bad jesture or picks up on something have you been around the two times your dog reacts to your dad the dog might be misidentfying your dad he might have some anxiety issues i would watch what goes on when your dog is this way to your dad and get the situation remedyed