Read the eyes

Is the cat frightened, or fighting mad? The eyes are a good signal. When a cat is frightened, the pupils of his eyes dilate. (And if you’re familiar with cats, you know those pupils can become really large.)

You may literally see red in the eyes of a frightened cat, because the retinal blood vessels may be visible through the dilated pupils. The pupils of an aggressive, angry cat will constrict rather than dilate.