I loved the line after Peggy has freaked out about the mouse and Don given up trying to catch up. He says, "There's a way out of this room we don't know about."

It's a quick line in a sequence that was overshadowed by a bunch else but essential to the episode and perhaps to the changes in store for Don and Peggy.

>I watched it three times, and finding out new things about
>it.

Just from running across a couple other sites, it's great to see how "universally" well-regarded this episode has been.