All their blood/have to get drawn

All their blood? that is very unclear, to what it might refer? Also what is "they have to get drawn" in this context? At 3:45 -I mean I've always said if you were to sort of think of torture experiments it would be a phenomenal one, because you sit there and sort of watch as your blood is sucked out of you I'm… and it's incredibly painful for cancer patients who go through hell with all their blood that they have to get drawn...