"Nah. I'm getting bored of talking to you."

[He leaned over slightly like he was going to pull the knife out but he twisted it around inside the doctor's hand slowly instead. Kirk did that for a couple, long minutes before he finally pulled it out. He studied the blade in his hand for a moment before lowering it to McCoy's face, wiping the blood off on his cheek.]

"If you move, I'll slit your throat."

[Which was a test to see if the doctor actually wanted to die.]