In the beginning of the book, Percy saves an Ophiotaurus from a net in the lake at camp. Percy named the creature Bessie, only to find out later that it was a male. When he meets Bessie again, he and his friends are at Hoover Dam. Percy is the only one who sees Bessie, so he goes by himself. The ophiotaurus was trying to warn Percy about something, but for some reason, he couldn't communicate with him.
When they leave Hoover Dam they go to San Francisco's West Coast to meet Nereus, "The Old Man of the Sea". Nereus told Percy how to find Annabeth and Artemis, who have been taken by Atlas. While they were there, Bessie showed up again, but this time Grover understood what it was saying. The ophiotaurus was the monster that Artemis left to go find. Eons ago, the Fates created a prophecy when Bessie was born that said, if you sacrificed the cow serpent, you would gain enough power to over throw the Olympians. Percy and his friends met in Olympus at the meeting of the gods and goddesses. They told the Olympians that Bessie needed to be kept safe.
When they leave Hoover Dam they go to San Francisco's West Coast to meet Nereus, "The Old Man of the Sea". Nereus told Percy how to find Annabeth and Artemis, who have been taken by Atlas. While they were there, Bessie showed up again, but this time Grover understood what it was saying. The ophiotaurus was the monster that Artemis left to go find. Eons ago, the Fates created a prophecy when Bessie was born that said, if you sacrificed the cow serpent, you would gain enough power to over throw the Olympians. Percy and his friends met in Olympus at the meeting of the gods and goddesses. They told the Olympians that Bessie needed to be kept safe.