Jessica Paré's "Zou Bisou Bisou" was the breakout moment of Mad Men's season premiere, but it's not the only time a character from the show has broken into song. Mad Men's gone to that well quite a few times, and in each instance, singing is dangerously revealing for the character and for the people watching him or her: It's as naked as anyone on this show ever is. Megan was beyond thrilled to sit her husband down and serenade him; we knew she considered herself happily married, but oh boy, she is happily married and doesn't care who knows, and that candid display of self-possession freaked Don out. More than the surprise party, more than the mess, more than the fear of getting old, Don panicked because he saw, maybe for the first time, just how free Megan is with herself, how unlike him she is, how liberated she's capable of feeling. Megan's inner self is almost shockingly confident — and it scared Don, because that makes her a lot harder to manipulate. When anybody sings on Mad Men, they're their truest self, and that can be a terrifying thing to see.
Mad Men is a show about artifice, how we convince other people that who we are is who we are, how we manipulate people's wants to seem more desirable or right, how people lie to themselves and each other all the time, just to get through a day. But singing punctures that, and suddenly we see the man (or woman) behind the curtain.
Here's Joan doing "C'et Magnifique":
Joan is humiliated, frightened, trying to be resilient, and she holds the act together perfectly — until she can't, and she glares right at her piece of shit rapist husband (at :42), and we, and he, can see all of her rage and anguish. It's not the only time Greg has put her on the spot, and it's not the only time he's been incredibly unsympathetic, but this might be the first moment where he realizes that his abhorrent behavior has actually hurt or even affected her.
"My Old Kentucky Home" is actually the singing-est episode of the show, with Roger in blackface serenading a giddy Jane, and Paul trying to one-up his college classmate with a pot-induced sing-off. Roger's performance charms his new bride, but Don's disgusted. Oh, not by the racism, but by Roger's desperation. Roger thinks he's being silly and showing off what a ham he is, but what's really happening — and what Don sees plainly — is that Roger's baring just how pathetic he is, how deeply he needs Jane's fawning, how much he relies on the idea that he is, to someone, impressive. Don's often put off by Roger's preening, but rarely does he straight-up walk away, as he does here. Paul's performance similarly reveals to Peggy just how competitive and anxious Paul is. He thinks he's won a dick-wagging contest against his former foe, but what's happened is that Peggy sees him as slightly pitiful.
Sometimes the singing happens in private, and then it's even more revelatory. Peggy sings the opening song from Bye Bye Birdie to herself in "Love Among Ruins," and she's suddenly overwhelmed with both shame and confusion. Oh, this isn't me, she realizes — she doesn't even know the words to the song. To be sexy, at least in Peggy's mind at the time, she'll have to be someone else. Which is why she uses Joan's pickup lines later in the episode.
It's not just our regulars, either. In season two, we see Peggy's new parish priest Father Gill (Colin Hanks) sing to himself, too, and he also doesn't quite know the words or rhythms of the song. He's just as lost and scared as Peggy is, maybe more so, and he takes off his collar before he starts to play — demonstrating just how conflicted he is about his budding role as a priest. He knows he's out of pace with the people who should be his peers, so he's singing a song alone that's supposed to be sung as a trio. Ah, poor Father Gill.
Dancing, weirdly, winds up being the opposite: When characters dance, it's their most projected selves, their highest aspirations. Pete and Trudy perform a thoroughly choreographed Charleston in the hopes of appearing fun and carefree, all while Pete's dying to be accepted and Trudy's in agony over her infertility. Peggy wishes she were seductive in "The Hobo Code," so she tries to dance seductively. In "The Little Kiss," Peggy wants to feel a little superior to Megan, so she dances ironically.
Megan isn't dancing ironically, though. She's dancing openly, freely — beautifully, enchantingly. She sings the same way. She's the only character who wants to be who she actually is.