MEREDITH: "Human beings need a lot of things to feel alive."
GEORGE: "Family."
CRISTINA: "Love."
IZZIE: "Sex."
DEREK: "But we only need one thing"
RICHARD: "To actually be alive."
CRISTINA: "We need a beating heart."
ADDISON: "When our heart is threatened"
ALEX: "We respond in one of two ways."
GEORGE: "We either run or-"
IZZIE: "We attack."
RICHARD: "There's a scientific term for this."
ALEX: "Fight..."
ADDISON: "...or flight."
MIRANDA: "It's instinct."
MEREDITH: "We can't control it."
IZZIE: "Or can we?"

-grey's anatomy'