What was up with the mouse and the cockroach?  Or were they just ways to lead into the next line or scene?  (Doubtful)

After seeing the mouse for the second time, Don says, "There must be some way out of this room we don't know about."  Definitely a loaded statement.  I forgot what he was doing the first time he saw the mouse... can anyone remind me?

Then when they see the cockroach at the diner... Peggy: "Why is there a dog in the Parthenon?" Don: "That's a roach.  Let's go somewhere darker."  Are they playing on that juxtaposition as an analogy for the flaws of admen/women in comparison to how society receives their ideas?   Or maybe I'm overthinking it...

I said somewhere on another thread that I wondered if the idea of alcoholic dt's was being suggested.  Don could start seeing vermin everywhere.  He's got a very serious alcohol problem.

I think it may have been a reference to their "pests".  Sterling pestering Don to join him, Peggy's boyfriend pestering her all night too.  It was so hard for them to get away from their pests.