You're using animal blood.
Black eyes glanced over to the deer that was still bleeding out. It's legs twitched and it's tongue lolled out of it's mouth. A sigh and the dark eyes returned to the chalice filled with thick blood.
"I'm watching Murdock, as you said. He lives in a small town. Anyone I kill will be noticed," was the soft reply. "He's coming along well. He's full of hate for this place."
'I'm sending someone else to watch Murdock. I want you on the Winchesters.'
A swallow. The Winchesters were formidable Demon Hunters. Infiltrating them was signing your own release to Hell. If there were even the slightest hint that you weren't who you said you were, they'd follow that until they cracked you open like an egg, and then they'd send you spiraling back down into the frying pan. No demon wanted to watch them. They were good at what they did. Too good for anyone to go in and play pretend for more than a few hours.
'You're good and you're the only one I trust to pull it off.'
"Yes, Sir. Is there anything specific you wanted me to get from them?"
'I want to know everything. Bed one of them if you have to and leave nothing out. Don't pull out unless it gets too hot. If it does, jump your body and get out. I need to know where Sam Winchester stands.'
"Yes, Sir."
'Don't fail me.'
"I haven't yet."