"Bitter clusters ('ashkeloth') are theirs": your great men, whose awe "hangs" over you as a cluster. ("eshkol" connotes "greatness," as in (Michah 7:21) "There is no eshkol to eat, no 'ripe one' that my soul desires. The saint is vanished from the land, etc."
(Devarim, Ibid. 33) "The venom of snakes is their wine": The saintly and upright among you — their venom (of retribution) is as that of snakes. "and the cruel gall ('rosh') of asps" (is their cup of retribution): Your heads ("roshim", as in "rosh") (will be "bitten" by the cruel foe).