I hate to say it, but if Tru-leigh wanted to make sure to get all of Joachim's blood, he'd better have run out of there with blankets, sheets, and probably the whole mattress. On the other hand, when the guards most likely throw out the blood (after all, who needs that when they've got the body as evidence of probable murder-kidnapping by Jobe and Tru-leigh) the bed may be a suitable secondary source of blood... assuming Jobe and Tru-leigh somehow manage to escape their current predicament and likely future beheading.