To borrow one of the oldest lines in the book: Who are you, Jackie Peyton? And what have you done with the title character on Nurse Jackie we've gotten to know over the last three seasons?

On "The Wall," Jackie made the abrupt decision to leave rehab against her counselor's orders. And she returned to a changed All Saints as a very changed woman, chatting casually with patients, turning down drugs and - in one of the funniest scenes to date - shedding tears over Coop's critique of her hair.

So now I'm gonna feel stuff, Jackie asked O'Hara through her sobs, reminding me of the Seinfeld episode where Jerry wondered about the the "salty discharge" emanating from his tear ducts.

It was a funny moment, it was an incredibly well-played moment by Edie Falco and it was also a revealing moment.

Because if there was one word I'd use to describe Jackie up until now, it would be: numb. That's what drugs do to you, right? They numb you to the pain, even when you're bringing that pain down on yourself. Jackie really has been wandering through her life in a kind of trance, only peripherally aware of her actions.

But now? Her eyes are open to absolutely everything, even cracks from Coop, and it's an extremely welcome change for a show that had been running in place for three seasons. Is Dr. Cruz right that people simply are who they are? That seemed to be the message Nurse Jackie was sending for awhile, but maybe now it's not so clear.

Other thoughts on a strong episode:

• Another appearance by Carmelo Anthony. A Rex Ryan reference. Is the show trying to broaden its demographic?
• Seriously, Lenny, put a ring on it! Otherwise, you may lose sexy Zoey to the next policeman who walks through the door.
• I noticed, Coop. I'm very glad you shaved the goatee.
• Is it true that cats don't give a shit? I wasn't aware felines were that relaxed about life. Pretty sure Coop meant to say "honey badgers" there.

I leave you with a few of the best Nurse Jackie quotes from the week and ask for your take on the installment:

Jackie: Do you know who the father is?
O'Hara: No. I want it to be a surprise. | permalink

Jackie: Coop hurt my feelings. He basically said that he never liked my hair... so now I'm gonna feel stuff? | permalink

Zoey: How do you make every outfit look like pajamas? | permalink

Zoey: Every 12 days, I go through this thing where I wish you were a completely different person for 24 hours. | permalink

Jackie: Who's Rex Ryan?
Thor: Head Coach of the Jets, hello! You people are barbarians. | permalink

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.