Look where the arrow is pointing. That’s not part of the octopus; that’s a black marble jawfish pretending to be part of the octopus since her coloring fits so well.
But the octopus herself is also a first-class mimic. She can look like a sea-snake by pushing six of her arms down a hole and waving the other two like they’re one long sea serpent. She can turn into a flatfish by folding her arms into a leaf shape and waving them up and down. And she’s been seen mimicking lionfish, sea anemones, jellyfish, and more.
Octopuses are the most intelligent of all cephalopods. So they know what they’re doing. Here you see the octopus tootling along on the seabed and being joined by a jawfish:
For more information on the octopus and the jawfish, see the paper (with photos and illustrations) in the journal Coral Reefs.