Here is one of the many reasons why there is not an exhaustive list of things to check on preflight inspection. You just walk around that airplane and poke bits of it until you're satisfied that it is airworthy. You'd think that would have included spotting a cat in a translucent wing, but apparently not. The cat seems less upset about the whole experience than the typical cat is about vacuum cleaners, hair dryers, or a change in cat food brand.
I have unexpectedly found cats in or on an aircraft on three occasions, but two were in the hangar and one was a cat in a cage that was part of cargo, and the PIC knew it was on board. Current boss won't let us get a hangar cat. We had to settle for a hangar fish, which doesn't do much about the mice and birds.