The flaperons on the 787 go through certain motions once the TO/GA is pressed. I've always seen it when the 787 is viewed from behind on takeoff. The motions are completely symmetrical, i.e., not related to pilot inputs.
I'm wondering why they're programmed to do that. The primary flight computers (PFC's) go through a complete self-check after every flight. Testing the ranges of motion is done by the crew after engine start-up. Seems like the wrong time to run a test.
The drooped outer ailerons do not go through a similar 'check'. My thoughts: calibration for their position, or drag reduction during initial roll. The latter would not explain the full down deployment though.
The frames below are from an on board video for a clearer image: