I think the answer is:
E
Explanation:
! Think of the two parts as two tiles like in a shuffle puzzle, then the pattern goes flip slide slide, flip slide slide. The GIF below (made by @Decent Dabbler) demonstrates the cycle. ! [![Flip Slide Slide][1]][1] [1]: https://m.imgur.com/mganem6?r ! Huge shout out and thank you to @Decent Dabbler for making the GIF for me.