Any cat owners amongst my readers will undoubtedly know about the strange propensity of cats to climb into boxes. Apparently it works for cats of all sizes:
A well-known phenomenon to cat owners is the tendency of their cats to sit in enclosed spaces such as boxes, laundry baskets, and even shape outlines taped on the floor. This investigative study asks whether domestic cats (Felis silvestris catus) are also susceptible to sitting in enclosures that are illusory in nature, utilizing cats’ attraction to box-like spaces to assess their perception of the Kanizsa square visual illusion... [T]his study randomly assigned citizen science participants booklets of six randomized, counterbalanced daily stimuli to print out, prepare, and place on the floor in pairs. Owners observed and videorecorded their cats’ behavior with the stimuli and reported findings from home over the course of the six daily trials... This study revealed that cats selected the Kanizsa illusion just as often as the square and more often than the control, indicating that domestic cats may treat the subjective Kanizsa contours as they do real contours.
It's a fascinating result, and indicative that other animal species see the world much as we do. It still doesn't explain why cats like to sit in boxes, though. I think my conclusion ("cats are weird") covers it about as well as anything. But at least in one way, our perceptual/interpretive centers are just as weird as the cats' are. I'm not inclined to go sit in a box, but it does make me wonder what our pets would think if we showed them other optical illusions.
I doubt my dogs would be interested. If what they're looking at has nothing to do with food, petting, or playing, they pretty much ignore it. Must be nice to see the world in such simple terms.