هَرِجًا يَحُكُّ ذِرَاعَهُ بِذِرَاعِهِ قَدْحَ الْمُكِبِّ عَلَى الزِّنَادِ الْأَجْذَمِ
One humming fly rubs one foreleg against the other, like a person missing part of a hand bending over fire-sticks to kindle a spark.
The comparison continues the preceding fly image. The rubbing of its forelegs resembles a person bending over fire-sticks and working them together to kindle a spark. The analogy evokes motion and sound at once.