Isaac turns berserk for 10 seconds, replacing Isaac's tears with a melee jawbone club and gaining +0.4 Speed, some Tears, and +3 flat Damage.
The jawbone club works similar to The Forgotten's bone club.
Notes
The rune's effect is nearly identical to Berserk!, with the exceptions that Isaac will not get any speed bonuses from killing enemies, nor can the duration of the effect be extended. See the item page for more detailed information on the effect and notes.