Last night, Christina Aguilera played a game on "The Tonight Show" where host Jimmy Fallon challenged her to sing "This Little Piggy" in the style of Britney's to the tune of B-girl's debut single, "...Baby One More Time."
Then on Tuesday (Feb. 24), Ed Sheeran popped by BBC Radio 1's "Live Lounge," where he covered Xtina's Stripped classic "Dirrty."
Christina covered Britney, and then Ed covered Christina. Therefore, Britney has to cover one of Ed's songs (I'm thinking "Don't" with a little "Me Against The Music" flair?) before the clock strikes 12 -- OR ELSE.