The Black Eye Orb is a summon item in Dark Souls.
Found outside Anastacia of Astora's cage in Firelink Shrine after Lautrec murders her, which triggers when either the Blighttown Fire Keeper Soul is collected by the player, or after both Bells of Awakening are rung.
When in the main chamber before the fight with Dragon Slayer Ornstein and Executioner Smough, the player will receive a notification telling them that the Black Eye Orb is quivering. At this point, the player may invade Lautrec's world to combat him and his two companions, a sorcerer and warrior. If the player successfully kills Lautrec, they are awarded Anastacia's Fire Keeper Soul. Restoring it to Anastacia's cage revives her and re-ignites the Firelink Shrine bonfire. Alternately, it can be consumed for five humanity or used to upgrade Estus Flasks, just like any other Fire Keeper Soul.
Similar to the Blue Eye Orbs, the Black Eye Orb can be used if the player is in Hollow form.
A Black Eye Orb was also designated for Shiva of the East originally, but was removed before the final game was released.
The cut Black Eye Orb is displayed as Black Eye Orb (Shiva) in the ingame inventory. This orb is only obtainable by modding or save editing and if used in the courtyard area of Painted World of Ariamis, you can invade Shiva as originally intended. Shiva will be accompanied by his bodyguard during the invasion event.