There is a planet called Vegavampira, and on this planet the only really intelligent animals are Vegan Vampires, but there is one problem, because they are Vegan, they will not kill, nor will they take blood or animal products without the animal's prior consent, however, as they are the only sentient beings on the planet that are intelligent enough to provide consent, they are unable to feed from the animals that live around them.
And to survive these Vegan Vampires must feed on the blood of non-Vampires, even though another Vampire would happily give consent for their blood to be given to another Vegan Vampire, the Vegan Vampires specifically need a substance to stay alive that is contained only within non-Vampire blood.
So here is the question, if they are unable to feed upon the other animals on the planet (as the other animals are not intelligent enough to give consent, and maybe they wouldn't want to), and Vampire blood doesn't do them any good, how will they survive?
Note: They will accept non-vegan produce if consent is given, or there is no being to give consent (that if it did not come from a being - animals, plants etc not included).