In the scene where Kendra is murdered by Drusilla, she is killed by having her Cardiac artery severed (or so it seems) and falls to the floor, bleeding profusely. Neither Drusilla nor any of the other vampires present in the library at the time are seen to feed on her after she falls.
However when Buffy arrives a few minutes later, Kendra is laying on the floor with the cut from Drusilla's nail visible on her neck but not a drop of blood can be seen on her hands, clothing, or on the floor around her.
Where'd it all go?