27. Thuban means a serpent. At other places, the Quran has used hayyatun (snake) and jaann (a small snake) to describe the snake of the staff. The interpretation given by Imam Razi is that the snake of the staff looked like a serpent from its big size and has been called jaann on account of its swift movement which is characteristic of small snakes.
28. Some commentators under the influence of the Israelite traditions have translated baida as white and have taken it to mean that the healthy hand when drawn out of the armpit became white as if struck by leprosy. But commentators like Ibn Jarir, Ibn Kathir, Zamakhshari, Razi, Abul Saud Imadi, Alusi and others agree that baida here means shining and bright. As soon as Prophet Moses (peace be upon him) took his hand out from the armpit, it made the whole place bright as if by the sun. For further explanation, see (E.N. 13 of Ta Ha).