What is the difference between a Nachash and a Shefifon?
Rashi #1: They are really one and the same, and the Torah refers to it as Shefifon because it makes a hissing sound (when it strikes). 1
Rashi #2 (citing Targum Onkelos) and Targum Yonasan: 'like a viper 2 that waits by the wayside and a cobra that lies in ambush on the path (of whom the nations are terrified and who strikes the Plishtim).
Rashbam: Like a snake kills all who pass by the wayside, so too, will the tribe of Dan kill all their enemies 6
Whose bite is incurable. Targum translates it as Churman (the term used by Arab doctors [Seforno]), because it destroys all. The Seforno adds that it is kills many in one go with its look and with its voice, which is why it characterizes Shimshon, who was capable of fighting the enemy.
Yerushalmi, Terumos, 5:8.
Likewise Shimshon, who fought on his own, unseen by his enemies as he suddenly swooped down upon them (Seforno).
The Rashbam does not comment on the details described in the Pasuk.
Why does Ya'akov compare Dan to "a snake by the wayside that bites the horse's heels causing the rider to fall backwards"?
Rashi, Ramban and Targum Yonasan: Because: The Torah refers to Shimshon as 'a snake by the wayside that bites the horse's heels ... ', because, just as a snake causes the rider to fall 1 without actually touching him, so too, did Shimshon bring about the death of the three thousand Plishtim on the roof without touching them. 2
Targum Onkelos: [Shimshon] kills the mighty men of the Plishti camp, cavalry and infantrymen; he destroys the horses and the chariots - and he causes the chariot-riders to fall backwards.
Rashbam: 'The enemy falls before them. 3
רש"י: על שם שהוא נושף: קשה ש'שפיפון' שורשו 'שפף', ו'נושף' שורשו 'נשף'?
גור אריה: שורשים שיש להם אות שנופלת ושתי האותיות הנותרות שוות- פירושן אחד ויש להביא ראיה מזו לזו.
רש"י: על שם שהוא נושף: גור אריה: למה נדחק רש"י לפרש כך?
גור אריה: יש לפרש [לא כרש"י] ששפיפון נקרא כך כי הוא הולך על גחונו ושף את הארץ.