Sforno on Exodus 7:15/ספורנו על שמות ז׳:ט״ו

1נהפך לנחש, not only in appearance but also in its movements. This is implied by the word ויבלע, “it swallowed” (verse 12). We encountered this phenomenon already in 4,3 when Moses himself fled from the serpent his staff had turned into.