While doing research in the Caribbean, marine biologist Roger Hanlon was pursuing a very large and fast-moving octopus (octopus vulgaris, to be exact) when it suddenly vanished behind a rock... and what the creature did next literally made him scream.
The clip below, courtesy of Science Friday, shows exactly what happened:
That's not special effects... that's nature, folks.
Later in the clip, you'll see that Hanlon's research specializes in the elaborate forms of camouflage used by octopus, squid and other cephalopods... but obviously none of that experience had quite prepared him for this little surprise.