‘ And Gideon said, “Therefore when the Lord has delivered Zebah and Zalmunna into my hand, then I will thresh your flesh with the thorns of the wilderness, and with briers.” '
Harsh though this may sound it was in fact comparatively merciful. Their breaking of the covenant with Yahweh strictly demanded death (compare Judges 21:10). It was like desertion in the face of the enemy. Gideon simply proposed severe chastisement to the leaders. Some have suggested that he proposed something more severe, their being trampled on thorns as the corn is trampled on the threshingfloor, indicating an unpleasant death. This would be supported by the fact of what he did to the leaders of Penuel.