So you know how vampire gifts can grow over the centuries? Well, Carlisle's compassion isn't quite a gift, but one fateful day he calls a family meeting...
Carlisle: *wearing sunglasses* I have something very important to share with you all.
Jasper: *nods* It's understandable. We all fall off the wagon at some point.
Rosalie: Yessss! This bumps me up to #1 Most Controlled Vampire of All Time!
Edward: *pinches bridge of nose* It's not what you think, just wait.
Carlisle: You misunderstand me. I have not "slipped", as you so delicately put it. My compassion has simply grown to the point where I can no longer bear to hurt innocent animals for my own sustenance. Science has shown us that animals are perfectly capable of feeling pain and loss, even grief in some cases. And while we have only identified rudimentary sentience in some few higher-order species, Star Trek 4 suggests that our methodology is lacking. So as my compassion has grown, and my understanding of personhood evolves, I can no longer therefore, in good conscience, continue to hunt even the lowliest of animals simply to nourish myself.
Emmett: You lost me.
Esme: *awe* *love* He's never going to feed again. I will support you, my love, in your new quest.
Carlisle: Alas, our kind is incapable of that extremity. But... *takes off sunglasses*
Everyone: Um.
Emmett: Dude, your eyes are fluorescent green. What'd you eat, caterpillars?
Carlisle: As I said, I now feel obliged to hold sacred the life of even the lowliest animal.
Alice: *peeks ahead* Uh oh...
Carlisle: I now subsist purely on the juices of fruits and vegetables. It's quite simple, really; more negative pressure is required to extract the juices from the firmer vegetables, but the bite-and-suck model still applies. It's much better when the produce in question is still "alive" on the vine, tree, or what have you. I hypothesize that the vivid green hue is due to the chlorophyll.
Bella: You know, I think I could do this. I'm a natural at everything.
Carlisle: I'm gratified to hear that. As the head of this coven and household, I will do my best to help you all in this transition.
Everyone:
Jasper: I'm sorry, what?
Edward: *begins a new era of vegetable angst*
Emmett: Did he just say WE have to start *&#$ juicing too?
Carlisle: Naturally.
Esme: Dear, when I said I would support you...
Carlisle: *arm around Esme* Yes, Darling?
Esme: I lied.
