Summoning Ghosts (Camp Half-Blood)

Demigods have the ability to summon ghosts. They do this by digging a hole in the ground, [1] adding something for the ghosts to consume, and then chanting in Ancient Greek for the ghosts to remember their past lives and return from their graves. [2] The ghosts will eat or drink the thing the summoner placed in the hole [2] and answer any questions the summoner asks. [3] The ghosts who have been summoned cannot leave until the summoner releases them. [4]

History
In the past people would summon the dead with animal blood, but Nico, the only person depicted actually summoning ghosts, wanted to be respectful. He used Happy Meals and Coke Cola. [2]