Um...you know how ভ্যাম্পায়ার can eat if they for some reason want to,right...?

ভ্যাম্পায়ার can eat food, but according to SM's books, they have to "cough" it up later since their bodies won't digest it. Plus, it tastes like dirt, at least to Edward.

Well, as their digestive system doesn't work (any of their systems doesn't work!) they can't wait for the খাবার to come out the right way... So they have to vomit it... Gross, but that's the way...

Hope this helps! =]