How Well do Dancing's Derek Hough and Nastia Liukin know each other?

Nastia Liukin and Derek Hough have been Dancing with the Stars partners for two months, which is plenty of time to get to know one another... or at least fire up Google. We dropped by the pair's tango rehearsal last week to put to them to the test. How did they do? Well, not to add insult to Hough's literal injury, but numbers still aren't his strong suit.

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