رَفَّعْتُهَا طَرْدَ النَّعَامِ وَشَلَّهُ حَتَّى إِذَا سَخِنَتْ وَخَفَّ عِظَامُهَا
I drove her at a pace like an ostrich fleeing at speed, until she had warmed up and the movement of her frame grew light and rapid.
Ṭard al-naʿām supplies the model of an ostrich’s fast run. Raffaʿtuhā conveys urging the mount into vigorous motion. Sakhinat refers to the horse warming with exertion; khaffa ʿiẓāmuhā vividly expresses lighter, nimbler movement rather than a literal change in bone weight.