S. R. Faruqi:

This verse is a masterpiece of wordplay, and of poetry as a language game. And what doubles the strength of this foundation is that in our classical poetry the basic things are theme and meaning, not emotion, feeling, experience, and so on. The poet tries to see that the theme-- which is based on metaphor, so that in any case it's based on emotion, experience, and so on, or evokes emotion, experience, and so on in the reader's mind-- would as far as possible be fresh, and the meaning would as far as possible be complex.

Great poets like Mir, Ghalib, Anis, Iqbal not only perpetrated, in the words of Roman Jakobson, 'organized violence' on the language, but didn't hesitate/fear even to, in Barthes's words, 'disfigure' the language. Thus we see that here Mir, making use of 'paper' for wordplay, instead of pech-o-tāb casually used pech-tāʾo . (For a big page/leaf of paper, the technical term tāʾo is used.)

This verse doesn't merely have the wordplay of kāġhaż and tāʾo . Consider the following additional wordplay: be-tābī , pech ( tāb can mean twisting, contorting, etc.); then, of be-tābī , pech , mār (to twist and turn is the characteristic of a snake). He has called the pen a serpent because it is black, and ink too is black (as the poison of a pen/snake is assumed to be); in this regard he has shown the paper to be twisting and turning like a snake.

In sarāsar there's the sound of a snake's slithering [sarsarānā]. Then, some snakes have poison that throws those who are bitten into convulsions. Thus when the serpent of the pen moved on the paper, then in the paper convulsions (=twisting and turning) arose. Since poison is a metaphor for ink, when the ink affected the paper (that is, made its mark on it) then the paper was necessarily affected.

There's also the point that the 'twisting and turning' of the paper is not simply hyperbole. In olden times, when envelopes were not customary, in order to keep the contents of a letter hidden the paper used to be folded in various ways. Sometimes the paper was folded into the shape of a bird, sometimes into the shape of a key; sometimes it was rolled into a long twisted tube. If we look at the verse this way, then the real theme is founded on 'elegance in assigning a cause'-- that after a letter is written it was twisted and turned, but the reason was that when the pen showed its effect on the paper, the paper too began to twist and turn like a snake.

Jamil Jalibi once said to me that this double-ghazal of Mir's was interesting, but a little half-baked [ḳhām-kārānah]. His point was probably that it had a lot of wordplay and 'theme-creation'. But wordplay and theme-creation are not a sign of half-bakedness [ḳhāmī] in the poetry, but rather a proof of its well-doneness [puḳhtagī].

Nasikh has made the pen into the rod of Moses and the Rival into a serpent; he's created a good theme:

ho agar siḥr-bayāñ dushman-e afʿī-ṣūrat
qalam apnā bhī ʿaṣā-e kaf-e mūsâ hove

[if he would be of enchanting speech, the serpent-like enemy
my pen too would be the staff of the hand of Moses]

Indeed, the word siḥr-bayāñ has a devastating affinity with the theme, and makes pleasing the abundance of words in the second line too (that is, instead of 'the staff of Moses', 'the staff of the hand of Moses').

FWP:

SETS == KYA
MOTIFS == WRITING
NAMES
TERMS == 'ELEGANCE IN ASSIGNING A CAUSE'; 'THEME-CREATION'; WORDPLAY

And all this wordplay is greatly enhanced, and made even more serpentine, by the clever use of the 'kya effect' in the first line. Four possible readings are fully operative (so that each works quite suitably with the second line):

=Did the pen-serpent write it? (a yes-or-no question)
=What did the pen-serpent write? (a question about content)
=How the pen-serpent wrote it! (an exclamation of surprise and awe)
=As if the pen-serpent wrote it! (why, that never happened at all!)

SRF points to the folding of the letter as a form of 'twisting and turning'. There's also the strong sense in which the ravishingly multivalent and protean tāb (of which tāʾo is a variant) evokes heat and fire, going back well into both Sanskrit and Persian. In fact that sense of 'heat' or 'burning' is what gives rise to the metaphorical meaning of 'agitation, anger, pain'. So the paper could well be contorted and curled because it is on fire.

And then as a finishing touch, we notice only retrospectively that the first line begins with be-tābī-e dil -- which makes the wordplay so convoluted that it's actually paradoxical. The state of be-tābī is a lack of tāb in the sense of 'strength, power, endurance' (think of the related tapas on the Indic side), so that the result is 'agitation, restlessness'-- in other words, just the kind of pech-tāb that the paper is showing. (See the definitions above.)

Or maybe the finishing touch should be the way sarāsar so hissingly evokes sarsarānā , 'to creep along (as a snake);... to hiss, to emit a hissing sound' (Platts p.654), thus adding some sound effects as well, as SRF has pointed out.

What a gloriously twisting, convoluted verse! How did the 'serpent of the pen'-- even Mir's pen-- ever manage to hold it still long enough to write it down?