In the always-apt words of Cher Horowitz, “Not a total Betty, but a vast improvement.” The second video off Britney Spears’s Femme Fatale, for the Ke$ha-penned banger “Till the World Ends,” tries hard not to make the same mistakes as the inadvertently depressing “Hold It Against Me.” There’s more dancing — though it’s still largely arm-related — and much, much more smiling. The smiling works, a sweet insta-fix for dead-eye (though it does conjure an imaginary scenario in our minds wherein someone is standing just off-camera yelling at Britney, “Smile! Smile! Smile more. Okay, now really Smize!”). The whole video supposedly takes place on December 21, 2012 (the day the world ends in Roland Emmerich movies and on the Mayan calendar) in an underground club one can only access through a manhole. Down in the thumping, subterranean hot spot everyone is gyrating around in a pretty dead-on imitation of the “I’m a Slave 4 U” video, with less sweat but a similar tendency to sexily twitch en masse. When the world finally does end, it’s with a big, bright light and some arty earth shaking — the neurotic in us got intimations of a nuclear blast, but then Britney climbs out of the manhole, into the sunshine, smiling with her mouth open.