Genesis 49:17 - Coke's Commentary on the Holy Bible

Dan shall be a serpent— The next word points out a particular kind of serpent: the Vulgate takes it for the cerastes, a kind of horned serpent, of a very subtle nature, which, Pliny says, hides its whole body in the sand, shewing only its horns as a bait to catch the birds: and this translation Bochart supports. Our version of adder seems as probable as any; because it is well known that this kind of reptile stings all sorts of cattle. Be that as it may, the comparison intimates, that the Danites were to be remarkable for stratagems of war, defeating their enemies more by policy than open force, like those serpents which lie in the road, and unexpectedly bite horses' heels, and make them throw their riders. Moses gives them the same character, by comparing Dan to a lion's whelp, leaping unexpectedly out of a thicket, Deuteronomy 33:22. We have instances of the Danites' policy in Samson's dealing against the Philistines, Judges 15:16 : in their sending the five spies to discover what part of their enemies' lands was weakest, and might most safely be attacked; and the destruction of the careless and confident inhabitants of Laish, or Leshem, is well represented by the rider's falling backward from his horse.