How does Percy show that he is a hero in Chapter 17 of The Lightning Thief?
In Chapter Seventeen of The Lightning Thief, Percy, Annabeth, and Grover are wandering around West Hollywood in search of DOA Recording Studios (the location that holds the entrance to the Underworld).
After a run-in with a group of wealthy kids with knives, the trio runs into a store called Crusty's Water Bed Palace. There they meet Procrustes (Crusty for short), who invites them to try out a few of the water beds. Annabeth and Grover do as he suggests, but Crusty suddenly binds the two to their beds with magical ropes that he summons by snapping his fingers and saying, "Ergo!" Crusty will only release Annabeth and Grover if Percy makes them fit their six-foot-long beds by stretching their bodies out. Percy realizes that this is the mythologically infamous "Procrustes the Stretcher" who attacks people by stretching them or amputating their limbs.
Percy shows that he is a hero in his ability to outwit and defeat Crusty. He convinces Crusty to lay down in one of his own beds and uses Crusty's own trick to bind Crusty to the bed. He then decapitates Crusty with his sword, Riptide, and frees Annabeth and Grover so that they may continue on their journey to the Underworld.