Genesis 49:17

Dan shall be a serpent by the way, an adder in the path, that biteth the horse heels, so that his rider shall fall backward.

Cross-reference

Judges 16:22-30 shows Samson's final victory, a serpent-like strike bringing down the enemy.

In Numbers 10:25, Dan leads the rear guard — echoing the serpent biting the horse’s heels from behind in Jacob's blessing.