Maru the Japanese Scottish fold is ten years old, but he still loves his boxes, no matter what they are made of. His roommate Hana is all grown up, and still taking lessons from Maru. In this video, Maru confronts a see-through box, or what we'd call an aquarium.
We can clearly see that Maru, like all cats, takes the shape of his container, and is therefore liquid. -via Tastefully Offensive