As Robert drags the female vampire's body into his station wagon, what does he discover that strikes terror in his heart? Chapter 4 I am legend

On his way out, Robert nearly trips over the comatose body of the man he had moved earlier and is startled to find that he now looks and smells like someone who has been dead for years. He realizes with a shock that the sunlight has killed the vampire. He wonders if the sun's rays have somehow affected the vampire's blood, and if the other things that vampires fear (garlic, stakes, the cross, mirrors) also affect their blood. He resolves to do some research on the subject. To test his theory, Robert snatches the body of a sleeping woman from a nearby house, flings her to the sidewalk, and watches her writhe and die.