فَلَهَا هِبَابٌ فِي الزِّمَامِ كَأَنَّهَا ۞ صَهْبَاءُ خَفَّ مَعَ الْجَنُوبِ جَهَامُهَا
When guided by the leading rein she surges forward, like a reddish cloud whose light, rain-spent mass is swept quickly along by the south wind.
Hibāb denotes energetic, rapid movement; zimām is the guiding rein or rope. The cloud simile is primarily about swift motion, not a claim that the animal and cloud share an identical shape.