Tafsir of Ash-Shu`ara' 26:32

(He threw) Musa, after Pharaoh said that to him, (his staff, and behold, it was a serpent manifest) appearing clearly in its snakelike nature; meaning, it was not a deception or an illusion as the sorcerers do. The thu'ban (serpent) is the greatest of all snakes. Its etymology is derived from tha'ba al-ma'u (the water flowed), meaning it flowed with a wide, expansive flow. It was named as such because of its swift movement without legs, as if it were flowing water.

The manifest meaning is that the staff itself transformed into a serpent. This is not impossible if it occurred by the removal of the quality that made it a staff and the creation of the quality that made it a serpent, based on the view of some theologians regarding the homogeneity of substances and their equality in receiving qualities. The only impossibility would be its transformation into a serpent while still remaining a staff, due to the impossibility of one thing being both a staff and a serpent at the same time.

It has been said that this occurred by the creation of a serpent in its place, but the manifest wording of the verses makes this view unlikely. Reports have arrived indicating the immense size of this serpent, and nothing is beyond the power of Allah Almighty. The explanation of the nature of the situation has already been provided.