A/N: This whole story is definitely mine. The lecture on vampirism isn't my friend Lyra's and I didn't tell her I'd give her credit for it. It's mine. Just getting that cleared up.
It was a normal day in the Cullen household. Basically, everyone was swooning over their respective sweethearts. Since I'm too lazy to name them all, I'll just assume you already know them.
Suddenly, things took a not-so normal turn.
A knock at the door was the first unusual thing. The Cullens didn't get many visitors. For a moment, they stared suspiciously at the door. Then, finally, Alice bounced up to get it.
The second unusual thing was the girl at the doorway. She looked normal enough, but the way she stared at them was uncomfortable. Not to mention that she was a perfect stranger. Perfect strangers very rarely, if never, came to the Cullen house. "Hello," Alice tried hesitantly. The girl paid no attention. Instead she asked, rather brusquely, "Are you the vampires?"
There was a collective gasp at this highly not-normal statement. The girl nodded, not put off in the least. She strode past a dumbstruck Alice, tossed her coat on to a chair and stood before the family, hands on hips. "You," she declared loudly, "Should not exist."
A murmur passed through the room. Who was this crazy kid? How much did she know? What was she talking about? Why did she wear those shoes when they clashed so badly with her top? The girl, unfortunately, gave them no time to decipher these mysteries of the universe. Instead, she launched into full lecture. "You vampires simply cannot exist," she scolded, wagging her finger at Emmett, "It's either that or you are somehow following the laws of a parallel universe. Being someone who hates scientific incorrectness, I've been looking over each of your physical traits, tsking and slapping my forehead at each detail that's wrong." She paused for a moment of silent despair.
"Your venom is a substance that sort of turns normal human cells into indestructible stone. Skin cells, hair cells, stomach lining cells or whatever cells you can come up with have their chromosomal count (upped from 23 pairs to 25 pairs) altered, their organelles rendered inactive and the cell as a whole becomes virtually indestructible." She gasped, melodramatically. "But wait! Somehow, without ANY source of energy or simply any 'by-products' (you are somehow 100% efficient), you can move at super speeds, have spectacular senses and simply unimaginable strength. So what we are looking at is pure energy out of nothing."
Carlisle tried to say something, but the girl cut him off, speaking a little louder than before. "Oh, but wait! I'm forgetting something! You vampires drink blood! That's where your energy comes from! Unfortunately, most of blood is plasma which should be generally excreted by the body. And coming back to the whole indestructible cell thing, how in the world are your cells supposed to absorb the blood if their walls are impenetrable? And if they are not, then what makes them indestructible? This vampire venom (if existent, I mean) is probably as puzzling as the working of a black hole. Technically, the consumed blood should simply be sloshing about in your blood vessels, unable to be absorbed. You are not simply creating energy out of nothing, and inhuman amounts of it. Meh." She seemed highly disapproving.
"Anyway. Back to the alteration of cells. Somehow, your eye color changes to red (drinkers of human blood) or brown (drinkers of animal blood) and your eyes become darker and darker depending on the amount of time since your last blood binge. I'm pretty sure something is freakishly wrong with your irises."
"Excuse me?" Rosalie tried saying, but the girl cut her off too, practically yelling now. "And what about transformation? Suddenly, during the few days when the vampire venom is ravishing your body, all your features alter to become the epitome of exquisiteness. All cuts, scars, wounds, bruises, broken ribs, snapped necks and what not suddenly vanish. What IS this stuff? It's as if the venom knows exactly what humans feel attracted to and turns you into horrifyingly "beautiful" beings." She made very obvious air quotes. Rosalie looked highly affronted.
"Excuse me," Carlisle finally managed to butt in as the girl stopped to take a breath, "But you do realize we're works of fiction, don't you?"
Now the girl looked downright disgusted. "Breaking the fourth wall, now? What is wrong with you people?" She grabbed her coat and pulled it on while stalking out the door. It slammed behind her. Nobody was sorry to see her back.
For a moment, there was silence.
"Well…" Emmett finally said, "What now?"
And the normal day continued.
A/N: Ha! The lecture is Lyra's! Bet you never guessed that!
Okay, I'll stop now.
Thanks very much to Lyra for her genius explanation as to why Twilight vampires scientifically cannot exist.