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When Percy, Annabeth, and Grover meet Persephone and the hellhounds, Persephone tells the hounds "fige" and "makria tous". This is Greek for "leave/go away" and "away from them", respectively. Also, when she calls the hounds back, "éla edó" meaning "come here", also in Greek.
Rick Riordan, who wrote the Percy Jackson books, hated the script and has never seen the complete film. But he still accepted the paycheck from the studio for the rights and has stated he is grateful for how many people discovered the books because of the films. He also strongly advocated for the novels to be readapted, which would later happen with the Disney+ series Percy Jackson and the Olympians (2023), for which he wrote most of the teleplays.
Rick Riordan has called the movie his "life's work going through a meat grinder." However, he also has stated that his problems with the movie lie with the script- he does not blame the actors and personally thinks they are quite talented. He even said he feels sorry that they were dragged into the film.
In the Parthenon Museum, Annabeth (Alexandra Daddario) begins telling Percy (Logan Lerman) a story about her mother, Athena. The tale she suggests is the Greek myth about how the capital city, Athens, got its name. The city's citizens were arguing over which god, after whom to name the town. The two choices were Athena and Poseidon, Percy's father. Both agreed that they would bestow a gift onto the city, and whichever gift was deemed more useful, that giver would have the town named after them. Poseidon struck his trident into the ground and created a spring from which the townspeople could use the water. Unfortunately, the water turned out to be too salty and therefore useless. Athena presented a single olive tree. The people realized the tree had many uses: Its fruit for eating, its wood for building and burning, the oil from its fruit for cooking and bathing, and the pits of the olives could be planted, bringing up more olive trees. The people agreed the olive tree was more useful and named the city "Athens" in honor of Athena.
When they drive off from the casino, they are in a Maserati, which happens to have the trident as an emblem.
In Greek mythology (at least in the classical version), Athena is a daughter of Zeus, which makes Annabeth and Percy first cousins once removed. However, Percy states in the final book the gods don't technically have DNA, and it doesn't exactly count. For example, two Hermes kids dating would be like dating your sibling, but a Hermes kid and Ares kid are okay.
Ray Winstone: As Ares at Olympus. In some shots, you can see him sitting on his throne in between Demeter and Athena, whereas in others, he's gone.