They are hitting the plexiglass in front of the camera and crabs, so I assume it's nothing interesting to look at science wise.

I thought when the cuttlefish starts blinking, it essentially becomes invisible to the crab

a video has nothing to do with a brain

The video is representing what a crab sees. An abrupt cut is either implying that the crab stops seeing (for brain damage reasons), or the video is not quite living up to the promise, and they are asking which it is.