Dean saw the effects of his taunts and anger, it pushed her to breaking point. He slipped his knife into his hand, waiting for her to strike.
She didn't.
In the back of his mind he knew what would happen once Sam came in, the chastising and disapproval, but he couldn't care about that right now. The Mark was burning on his arm, blood stinging in his veins, urging him to leap forwards and make the first move.
The standoff grew more and more tense, with each passing moment it became more appealing to him to attack. He watched her carefully, taking note of the way her muscles tensed and relaxed and the slight tick in her jaw as she fought for control.
The outside door to the Bunker opened and closed with a loud booming echo, and Sammy's footfalls could be heard coming down the steps. In a few seconds his brother would come down to the balcony and see them below, assuming the worst...
In a split second, just before Sam was in sight, Dean tucked his knife away, holding his hands up in a peaceful gesture. He saw her eyes register the non-verbal communication and she relaxed, pulling out a chair and sitting on it. She appeared calm, but he could see her fingers clasped in her lap, taught as she had just been.
Sam gave a loud sigh as he came down the last of the stairs. "It's good to be back," he said, giving Dean a heavy hit on his shoulder as he walked past. "Miss us?"