Why does the dead body in the first Twilight film trigger in Bella the thought that Edward is a vampire? It seems really random at the time.

In the movie version, when Bella and Edward are returning home from Port Angeles, they notice the emergency vehicles and lights at the sheriff's office. When they stop, they discover that one of the local men has been found murdered. As she is walking out of the sheriff's office, the dead man's body is being placed into an ambulance, and Bella notices his uncovered foot. The skin color is very pale, which reminds her of Edward's coloring. She's a smart girl, and all the odd things about Edward start to come together in her mind. At home, she does some Internet searching, especially of the legend Jacob had told her about.

The next morning, she leads Edward into the woods and confronts him about what she knows: his skin is pale white and cold like that of a dead person; he never eats; he doesn't go out into sunlight. He must be a vampire!

So, you see, it's really not all that random.