Nocturne for Violin and Cello

[Lizzie]

Yay! Finally a Tyger poem! I come from a musical family, so this one makes my heart happy.

The title is perfect. Evening and intimacy -- the male being the bigger instrument and the female has the higher pitched, whinier voice that sounds like a cat being murdered if you don't play her just right. Works on every level.    You may get push back from some who think you are unfairly stereotyping, but those people can write their own poem. Yours is lovely. 

Nocturne for Violin and Cello

To say that the hair 
of the bow is also
caressed

would be
to say enough
about the familiar

reciprocities. -- Yes, enough has been said. The opening flatters the reader by insinuating that they're smart enough to get it. A strong start. 
Still, they moan
so prettily, illicit -- Unfortunately, I don't think that "prettily" is the right word. Adverbs are usually a compensation for a weak verb, but "moan" is not bad. I would still revisit moan anyway to see if you can come up with a verb which wouldn't need a modifier. "Pretty" is one of those vague generalities that doesn't do as much to amplify the meaning of a word as much as one might initially imagine. "Beautiful" has the same problem. 

conspirators whose plans -- I agree with Mr. Alien that this characterization of the instruments as illicit conspirators isn't congruent with the idea of them playing beautiful music from the page. Perhaps there in an implication that this is an affair? Perhaps there was supposed to be a piano accompaniment and it wasn't invited to the party? We're now a hair away from the metaphor breaking down. Ultimately, it seems unfair to the violin and cello to criticize them for playing music the way they were intended to be played. They are sympathetic characters, in my opinion. 
are laid down -- Nice double meaning here
in dashes and dots. -- I agree again that "dashes" doesn't work. "Dots" works -- you have a lot of options here. 

Do you think
it would be more crude -- Why would it be crude? I experience this as an unpleasant authorial intrusion -- I stopped to think, "Is this crude? What would make it crude? Should I feel that it is? Does the author want me to think it is or isn't? Am I being asked to weigh in one way or another? Is this an attempt to displace guilt onto the reader, like a hot potato kind of situation?" This question led me off on several tangents that added nothing to the reading. 
to say he is played

between the legs
or that she
is tucked away, -- I like this observation that the cello and the violin are not so different 

inches from a kiss? -- I think that the eroticism is clever and tastefully done. It doesn't need an apology. I mean, is Sharon Olds crude? In my opinion, no, but it's up to you where your personal lines are. Either way, you can't expect the reader to make those decisions for you. 
Even now, distending
and collapsing

like a lung, they intend -- I get the point about lungs vs. string instruments. I don't have a solution for this. I really like the image and don't wish to see it cut, but I can see the inconsistencies for the conceit. It fits with the tone, though, so I'm waffling..... I suppose there's no harm in trying to think of a different image to resolve the tension, as you can always stick with the original if there's nothing better. But, yes, this would work better with woodwinds or brass. 
to play back their secrets -- "play back" could be substituted with a more interesting verb
only to themselves. -- Is this the illicit part? That they've left the orchestra behind? I like the idea of a couple of instruments sneaking behind the curtain after a performance and doing a bit of avant-garde exploration. It seems innocent though. If you were looking for complicated, it doesn't come across to me that way. However, I might change my mind next week, and then I'll come back if I decide I was wrong all day long. 

I hear a controlled tone to the speaker's voice, like a vocalist who's learned to modulate volume and master range. Reads as sophistication. And I like that it reads like a song from beginning to end. 

I think it has good bones (no pun intended). I hope you keep working on it. 

Best,

Lizzie