Score one for anxiety-inducing forces of nature. Gravity, Alfonso Cuarón's latest thriller, starring George Clooney and Sandra Bullock, swept the weekend box office, taking in $55.55 million on its opening weekend in North America alone. The attractive-astronaut thriller also took another $27.4 million overseas. The movie kicked Cloudy With a Chance of Meatballs 2 into second place, scoring the biggest-ever October opening to boot. Rounding out the top five are Runner Runner, Prisoners, and Rush.