A hunt is not successful if no blood is gained, even if the hunt action is still successful.
101926
Tainted Vitae
Only usable if a vampire controlled by your predator is about to successfully hunt.
The hunting vampire gets +2 hunt this action and put this card on them; you still control this card. The attached vampire must burn 1 additional blood to announce a bleed action (if it is not canceled as played) against you.
Rulings
The hunt bonus applies to non-standard hunt actions, blood comes from the target of the hunt.