Most of us know the routine by heart: seat upright, tray table stowed, window shade open, bag under the seat. Meanwhile, flight attendants make one last trip through the cabin before strapping themselves into their unusual little seats. Almost none of these rituals are arbitrary. Many exist because takeoff and landing are moments when the cabin must be ready to go from ordinary flight to emergency response with almost no warning. Here are 12 things that cabin crews are actually doing, and why.