Two of this summer's biggest pop hits sound remarkably alike. Katy Perry's "California Gurls" has a choppy piano/guitar riff and a driving beat: so does Ke$ha's "TiK ToK." Perry's song has an "Oh, oh, oh," refrain at the end of the chorus; "TiK ToK," features a similar vocal melody. In this video clip, an Australian radio show plays a mashup of the two songs, just to show how similar they are.

The similarity may be due to the fact that both the songs were written and produced by Dr. Luke, an American music producer who's also penned hits like P!nk's "U + Ur Hand," Kelly Clarkson's "Since U Been Gone," Britney Spears' "Circus," and Flo Rida's "Right Round," which also features Ke$ha on guest vocals. Dr. Luke also produced and co-wrote many of the tracks on Ke$ha's album Animal.