The Fermented Spider Eye is a potion ingredient used to brew potions with negative effects. It can be crafted from a spider eye, brown mushroom, and sugar on a crafting grid. They are inedible, unlike the regular spider eye. As drinking any potion with a negative effect yourself is quite a silly thing to do, the potions are often brewed into a splash potion with gunpowder, making them throwable weapons that inflict their effects on mobs/players instantly. However, throwing the potion too close causes the player to suffer from effects too.