Laughter can be caused by the comprehension of an absurdity, a frustrated intention or by something that violates a norm. I would not readily ascribe this sort of comprehension to the aforementioned animals and would be careful not to anthropomorphize other species, as tempting as it might be.
I was left in no doubt -- none whatsoever -- that they were laughing at the absurdity of what I evidently considered "swimming".
Maybe I'm anthropomorphizing them... but I'm pretty sure they were dolphopomorphizing me first, and it was cracking them up.
Anyhow, those dolphins were a bunch of punks.
There have a been a few knows cases of it. https://www.theguardian.com/science/2004/nov/24/internationa...
Karl Popper's four functions of language might help here. Language has an expressive function, a signaling function, a descriptive function and an argumentative function. No other animal besides Man shows any sign of the anything but the first two, but it's the second two that require abstract concepts. These animals may very well possess imagination, but imagination is essentially concrete. You don't imagine Triangularity, but rather specific triangles (though in human beings, by virtue of having an intellect, the image of a triangle is "accompanied by" the concept of Triangularity).