FWP:
SETS == DIALOGUE; PARALLELISM
GATHERINGS: {6,3}
LIGHTNING: {10,6}
MUSIC: {10,3}
SMILE/LAUGHTER: {27,4}
For background see S. R. Faruqi's choices.
The simile of the rain as tears, and thus of the rainclouds as weeping, is obvious. That of lightning as smiling or laughing (since ha;Nsnaa has both meanings) is based on the flash of brilliant white teeth as they are suddenly visible in a smile or laugh. (And of course, the sight of the beloved's teeth dazzles the lover's eyes as lightning does.)
These white teeth should also be imagined as flashing against a suitably dramatic background of blackened gums, since the use of missii ('a powder composed of yellow myrobalan, gall-nut, iron-filings, vitriol, &c., used for tinging the teeth of a black colour', Platts p.1036) was very common in Ghalib's world. Admirers of Umra'o Jan may remember that the ceremony through which a :tavaa))if formally entered the profession was called missii lagaanaa .
Compare {212,1}, another verse involving a smile/laugh and a show of teeth.
Gyan Chand:
The raining-down of clouds has the similitude of weeping, and the cause of the weeping is restlessness: there is the wish for a gathering of happiness. The way a child weeps in order to cause some desire to be fulfilled, in the same way the clouds are weeping and insisting. The flash of lightning has the similitude of smiling/laughing, but it is momentary. The lightning flashes as if it is smiling/laughing at the clouds' request: how small is the interval of life! How would a gathering be able to be arranged in an instant! (492)