I've been reading some interesting articles on the subject of humour. Only recently have scientists been able to approach what makes us laugh, and the answer involves an expensive magnetic resonance imager.
One conclusion is that a sense of humour is proportional to intelligence. Smart people may not be funnier, but they can convince stupid rich people to buy MRI machines and fund science as to why a fake rubber turd on the boardroom table is hilarious.
Smart animals enjoy humour as much as humans. Birds, dogs, and lab rats, among others will laugh when playing.
The octopus is a remarkably smart animal. It is sensitive, emotional, and has a powerful memory. Normally, octopi are solitary creatures and seldom congregate. However, the octopi of the Italian island of Capri have formed social groups. Their territory is rich with warm, comfortable water but tourism and fishing have eliminated most of the food, so the octopi have a tough time scrounging enough to live. Worse, the area is teeming with deadly predators.
Most of the Capri octopi are around the size of a human hand, so they seldom pose a threat to anything larger than an anchovy. They will band together in loose groups to "farm" what food is available to them.
My wife showed me an amazing marine biologist's report of these little guys defending their territory. A predator eel was swimming into the octopus feeding area. Normally, a solitary octopus would change colour to blend in with the ocean bottom and squeeze into some tight hiding hole. The Capri octopi were much more aggressive, however. They formed what I prefer to think of as a "suction cup rodeo".
Working together, a couple of octopi remained in the open to lure the eel into the trap. From above, the bravest octopus gently glided onto the unsuspecting eel's head and covered the eel's eyes with its tentacles. Then, it hung on like a rodeo star while the eel tried in vain to buck the octopus off of its face. The little octopus hung on like a champion! The eel twisted, turned, and leaped much like a rodeo bull. The octopus simply applied more suction. Eventually, the eel had had enough and tried to swim away. Once the little octopus finally let go, the eel wasted no time in escaping.
The Capri octopus community watched this action from afar. Were they laughing? I don't think that's physiologically possible for an octopus. But I imagine they were amused! The plight of the eel, the vicious predator turned into a comic buffoon with an octopus glued to its eyes, is a classic comedy turnabout that occurs when the bad guy gets his come-uppance from the diminuitive hero. There's a certain amount of class struggle that went along with the actual battle: the octopi worked together to trap the eel, but they also were unified by the spectacle of their hero humiliating and defeating a hated foe that normally would have been much more powerful than all of them grouped together. Comedy becomes a means of social bonding, although we can only surmise the emotional state of the octopus by observing its skin colour at the time - octopi will change colour depending on mood. If the octopi found the sight of one of their number glued to the face of an eel funny - and it's pretty funny to us humans - then this would also reinforce their social confidence and create a powerful memory of the event.