Dean looks at Mary, eye to eye, making sure she's looking at him. He wants to make sure she understands why she can't, not now, not until he's back to normal. He hates having to say it, but it has to be said.

"Damn right you can't, Mom, he's possessed. I know you're a hunter, you were, but this demon ain't small fry, and I can't back you up with my ribs like this. So don't. Not now. Wait 'til this blows over."

He's working himself up, trying to sit straighter and insist she doesn't do anything that'll get her killed, ignoring the sharp stabbing pains running along his ribcage.