Passage: Percy is tasked with locating that bolt before an all-out war can break out. He chooses Annabeth and Grover to accompany him on a quest to the realm of Hades, the most likely culprit. Before he leaves, Percy is given Chiron's magic sword Anaklusmos ("Riptide") and Luke's flying sneakers. The trio then travels towards Los Angeles, the entrance to Hades's realm. Along the way, they are attacked by the Furies, Medusa, Echidna and the Chimera, and several other monsters. They also do a favor for the god Ares, who gives them a backpack full of supplies and transportation to Nevada. Percy gradually learns more about his companions, his powers, and the world of the Greek gods. When they arrive in Hades's realm, Grover is nearly dragged into Tartarus by Percy's flying shoes. The battered group finally meet Hades, who reveals that his Helm of Darkness has been stolen too. Hades accuses Percy of stealing his helm and threatens to kill Sally Jackson (who has been the god's hostage the whole time) and reanimate the dead unless it is returned. When Percy finds the missing master bolt inside Ares's backpack, the group realizes they've been manipulated. Narrowly escaping the Underworld, Percy challenges Ares to a duel. When the demigod wins, he gives the Helm of Darkness to the Furies; when Hades then realizes that Percy was not the thief, he returns Mrs. Jackson to their apartment in New York.

Question: What is Grover pulled by?
Percy's flying shoes