Sam froze as soon as he saw the Doctor's eyes. Black as night. He raised the gun, despite the common knowledge that the only person that he would harm by shooting his weapon was indeed the Doctor, and took a cautious step backward. "You don't belong in him," Sam started, expression growing dark.
He hated demons with a passion. And now, here he was, staring one down with a gun held out in front of him. He had other weapons on him that would be more useful against the demon (like Ruby's knife, which he had tucked away), but he didn't want to kill the Doctor. If he used the knife, it would instantly kill both the demon and it's host. They wouldn't go to heaven or hell. They would just be gone. Forever. Did he want that? For the demon he sure did. Not so much in the Doc's case.
He slowly reached into his jacket, fingers wrapping around a small bottle. He kept his hand out of sight as he stood rigidly on the spot, so the demon wouldn't have any idea that he was clutching at a bottle of holy water. "You're going back to where you came from," he said darkly.