"[And he threw it down,] and suddenly it was a snake, moving fast," meaning: it was crawling on its belly with speed.
﴿فَأَلْقَاهَا فَإِذَا هِيَ حَيَّةٌ تَسْعَى﴾ أَيْ: تَزْحَفُ عَلَى بَطْنِهَا بِسُرْعَةٍ.
