Season 2, episode 6: "Into You Like a Train"
"Into You Like a Train" begins with an inebriated Meredith, who believes that Derek has jilted her after her dramatic confession of love. (He was late, much to Meredith's chagrin.) The interns return to the hospital for duty after a massive train crash, which results in two strangers being impaled on a pole together. Bonnie, half of the injured pair, brings a lighthearted energy to the episode, despite her ultimately tragic fate. This episode's skillful marriage of humor and tragedy makes for a robust emotional experience.