Does anyone else find it funny that on a photography discussion board we're posting cat pics just like everyone on Facebook?
LOL. To test mundane stuff, they are excellent subjects: plenty of detail with whiskers etc, tonal if not color contrast.
And as models go, they are convenient and easy to find in a pinch... ubiquitous as the most common household pet in America. Easy to book a session, no need to sign releases, generally cooperative, and no need to pay them! What's not to love!!
As for the photography forum, setting the 'model' aside, the simple shot addresses high ISO/low light aspects of 5D3. Personally for me, the top left corner, pitch black in real life, was the key. It is clear much can be done with the interrelated banding/noise/color/DR issues in these rather extreme settings and 5D3 is fairly competent when pushed.