Sforno on Genesis 49:17/ספורנו על בראשית מ״ט:י״ז

1יהי דן נחש, a reference to a poisonous snake, one commonly called tzifoni, in Biblical literature. Arab physicians usually call such venomous snakes chorman. The name for such snakes implies that a single snake can kill numerous people at once, using both its stare, and it voice (hiss) which is heard and seen by many people. It is a fitting comparison to Shimshon who, all on his own, killed many people almost simultaneously.

2שפיפון, name of a slim snake; our sages use this when wanting to illustrate something extremely thin, “as the width of a hair.” Physicians claim that these types of snakes hide in the trees, their sting being felt as if one had been shot by an arrow. Shimshon’s mode of operation, an individual lying in wait, in ambush, is compared by Yaakov to this snake.