There are many startling videos of octopuses doing surprising octopus things. This video, by Flora Lichtman for Science Friday, is one of the most very all of that:
The scientist is Roger Hanlon. The octopus is nameless. (Thanks to investigator Susan Kany for bringing this to our attention.)
BONUS: From long ago, Bill Saidel and the perplexing flounder: To Sea, and Not to See