In Greek Mythology, Medusa was turned into a Gorgon when Poseidon, Percy's father, had sex with her in Athena's temple. Athena, Annabeth's mother, took offense and cursed her. Hence, Medusa's hatred for them, and her reference to unfinished business.
Athena was a maiden goddess (she could never marry), yet she had children, such as Annabeth, because like her, her children are born from pure thought, and given as a gift to the men she truly admires, therefore she is able to have demigod children, and still be a maiden goddess
When in the Parthenon Museum, Annabeth (Alexandra Daddario) begins telling Percy (Logan Lerman) a story about her mother, Athena. The story she tells, is the Greek myth about how the capital city Athens got its name. The citizens of the city were arguing over which god, after whom to name the city. The two choices were Athena and Poseidon, Percy's father. Both agreed that they would bestow a gift onto the town, and whichever gift was deemed more useful, that giver would have the town named after him or her. Poseidon stuck 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 for bathing, and the pits of the olives could be planted, therefore bringing up more olive trees. The people agreed the olive tree was more useful, and therefore named the city "Athens", in honor of Athena.
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 is okay.
When Chiron is calling for the campers to gather around to go over the rules for Capture the Flag, he yells for Dylan and Paris to stop "lollygagging". Chiron is played by Pierce Brosnan, whose two younger sons are named Dylan and Paris.
In the Greek myths, Persephone was abducted by Hades into the Underworld, but Zeus demanded her return on Earth. However, Hades tricked her into eating pomegranate seeds, and was forced to stay in the Underworld during the winter months, and returning to Earth the rest of the year. However, in the film, Percy Jackson had ten more days until the summer solstice to return Zeus' master bolt, and during the time, Persephone was seen in the Underworld at spring time.
In Greek mythology, the goddess Athena is a symbol of virginity. She never had any children. But in the books, it is said that Athena would create the children using her mind, being the goddess of wisdom. Adding in the traits of the father of the child and adding in some of her own.
The substitute teacher, Mrs. Dodds (Maria Olsen), writes, "I understand a fury in your words, But not your words", from Othello, Act 4, Scene 2, on the blackboard. Shortly thereafter, she turns into a Fury.
Uma Thurman (Medusa) interacted with several live snakes, with the help of a snake wrangler, in preparation for her role. Handling and holding snakes, she said, helped her imagine how it might feel for Medusa to have live snakes sprouting from her head.
In the book, there's a character at Yancy Academy named Nancy Bobofit. She is described as having red hair, pale skin, and freckles. A girl matching this description is seen in the background when Percy and his classmates are at the museum.
In the extras, when they're talking about Hermes, they say (incorrectly) that "he carries a Caduceus (two snakes, usually with wings, and entwined on a staff) which to 'mortals' is the symbol of Medicine". Actually, the Staff of Asclepious (one snake, no wings, on a staff) is the symbol of Medicine.
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.
The hydra Percy faces in the Parthenon Museum in Nashville was a creature in Greek mythology. It was the offspring of Echidna and Typhon. The Greek hero Heracles (known more commonly by his Roman name, "Hercules") defeated the hydra by cutting off most of the heads, save for the one immortal head, having his nephew cauterize the wounds with a burning torch, and burying the remaining head with a large boulder.
In classical mythology, the Lotus Eaters are a tribe of people who are in a nearly permanent stupor, because they consumed the seeds of a plant called "Lotus", and one of the many obstacles encountered by the hero Odysseus during his adventures in "The Odyssey".
In the book, the obstacles Percy (Logan Lerman), Annabeth (Alexandra Daddario), and Grover (Brandon T. Jackson) face are a fire caused by Furies, being tricked by Medusa (Uma Thurman), escaping the St. Louis arch, escaping a trap made by Hephaestus (Conrad Coates), and getting out of the Lotus Hotel and Casino. In the movie, the obstacles they face are escaping Medusa's lair, killing a hydra, and breaking out of the Lotus Hotel and Casino.
There are major changes from the book to the movie: Percy gets the pearls from a sea nymph in the book, but gets them by travelling all around the U.S. in the movie. In the book, there is a fight scene with Enchinda and a Chimera. This was deleted in the movie. The pantheon isn't in the book. Sally took Medusa's head and stoned Gabe, selling the statue. Instead, he opens the fridge and crumbles to pieces. There are many other changes.
In his disguise as Mr. Brunner, Chiron camouflages his horse legs using a wheelchair and a blanket to cover them up, with no explanation about how horse legs fit on it. In the original book is revealed that the wheelchair has magical powers, allowing that the horse legs turns in human legs to sit down on it.
Changes in book and movie: Book: 1. The trio fights Ares, Enchinda, the Chimera, and Hades, among others. 2. Annabeth is a blonde with grey eyes. 3. It takes Percy four months to find out Poseidon is his father. 4. Percy also fights a hellhound right before this. 5. Percy discovers his powers after fighting a Daughter of Ares named Clarrisse la Rue, and the camp is directed by Dionyus, God of Wine. 6. Percy also fights with a bully at his school named Nancy Bobofit. 7. Percy's pen must be uncapped to become a sword. 8. Luke takes Percy into the woods and nearly kills him with a scorpion. 9. Sally Jackson uses Medusa's head to turn Smelly Gabe into a statue. 10. Luke has a scar on his left eye. Movie: 1. They fight Medusa, the Hydra and others. 2. Annabeth has blue eyes and auburn hair. 3. Percy is claimed almost instantly at Camp. 4. There are no hellhounds. 5. Clarrisse and Mr. D are nowhere in the movie. 6. Nancy Bobofit is not a character as well. 7. Percy clicks his pen instead of uncapping. 8. Percy and Luke fight on the Empire State Building. 9. There is an after credit showing Gabe throwing aside a note from Percy, saying Don't open the fridge! Percy, and facing Medusa's head, and the screen goes black, followed by a crumbling sound. 10. Luke has no scar.