Nosferatu
Faith, Hope & Love
I think it's a little reminder to Eugene. "I think you're fucking useful - but I will not hesitate to fuck you up. So don't"
Dr. Carson didn't do anything wrong, but Eugene doesn't know that. I wouldn't be surprised if Negan knows Dr. Carson didn't do shit either, but he's all about fear=power.
Yeah, no question it was a warning to Eugene, that's why Negan told him to watch but my point is why waste a perfectly good doctor simply to make a point when they are not in abundance.
On a side note I am a big fan of Jeffery Dean Morgan but his character has become unbelievably annoying, the way he leans back when he says things, the fact that nearly everything is said as if it were meant to be funny has become almost impossible for me to watch.