I noticed that with two of them. It couldn't have been cum because they both spurted all of that clearly over his abdomen. I wondered if it was old engine oil (LOL) being used as lubricant. But it could have been poop juice, as you said. I know I would want a much cleaner hole than that to put my cock into. I wouldn't be able to keep a hard-on if I knew I was delving into poop!