My cat goes wild for... dog fur?

Two of our cats seem to enjoy the smell of my dog's fur. One in particular reacts to it as though it were a catnip toy. After I brush the dog, she goes after the fur-filled comb or the lumps of fur lying on the floor. She plays with it, rolls on it, chews on it, and goes absolutely wild. She rarely acts like that when given catnip. "Fresh" hair incites a stronger reaction. Can anyone offer an explanation?