After capturing crab prey, the octopus will usually kill them and hold one or several under the arm web, dissolve the cartilage holding the joints together, digest out the meat, and keep the exoskeleton bits. When it's finished, it will take the remains to the den entrance and jet the lot out into what becomes a midden. This water jet can be aimed also at a curious observer or researcher, as has happened to both of us when removing bits of prey remains to catalogue them, or just getting a hand too close to the octopus. What all this means is that the octopus has a lot of flexibility in using the water all around it to change its environment, that it can compute the effect of what is really a current for respiration and use it in a lot of ways. We discovered that this water jet could be used in a behaviour that's really far from what is expected of an invertebrate.
Octopuses can use the water jet to play, too.
We took on the challenge of deciding whether the term might also be applied to the octopuses. Play is an interesting area of behaviour, hard to define although we all know it when we see it. One category that seemed to apply to octopuses was exploratory play, including the manipulation of objects by an animal. Octopuses are well known for exploring and manipulating objects, so this seemed a likely transition. We gave Octopus dofleini at the Seattle Aquarium a simple object, a floating pill bottle that moved a little in the water inflow, to investigate during ten trials over five days.