You and your family were vampires. But nobody can know. You can tell if there is another vampire around you.

So one day while in calculus, the same class you've known for atleast 30 years.

But you got a new student. The only open seat was next to you at your table. When he sat down your teacher introduced him

Mr. Smith: "This is Jasper, be nice. He's new."

You look at him, studying him. Then you look at his eyes, you realized. He was also a vampire. All vampires have the same eye color.