Kaʾanna introduces a simile through a particle resembling a verb. ʿAlā al-matnayn minhu foregrounds the location at which the comparison can be observed.
Idhā intaḥā is a time clause associated with the horse’s turning movement. Madāk ʿarūs aw ṣalāyat ḥanẓal offers two alternate images of the comparable surface.
The sequence first gives the location, then the moment of motion, and finally the concrete object that renders the quality visible.