If every drop of blood is drained, how do they report back what happened? Is there a transfusion?
I would think that regardless of whether they consider us as no better than cattle, it would make sense to anesthetize subjects if for no other reason than to keep them quiet and make it easier to work on them.
1. There are persistent reports that some critters use FEAR to trigger brain chemicals in humans that serve as a super thrilling high sort of drug for the critters.
2. They can immobilize folks quite easily without anesthetic. The person is utterly immobilized,feeling all the pain, unable to move a muscle, sometimes can move their eyes.
3. Autopsies confirm what happened just as with cattle.