WARNING: The Hidden Achievement is for completing the game without using any hints, so be careful about that.

Some things before we start:

• Cats will be hidden inside drawers and boxes, behind doors, windows, planks and flags... Make sure you click on the objects in the location of the cat if you can't see it.
• Sometimes you'll have to click on multiple things to reveal the cat (e.g. a door and then a drawer).
• Grills that have smoke coming out of them have a lid nearby by their feet, clicking on that will make the smoke go away.
• The puffs of smoke coming out of the train will move away when you click them (they will not cover any cat when they move).
• Turn on the fan (follow the power cord to the outlet and click that) and click on the parachute to make one of the cats show up.
• Click on the projector to see the cat on the movie screen.
• There are 2 cats being blocked by moving bits on the screenshots, I have circled their positions.
• There are 2 cats missing from the last image (Far Right), those have arrows pointing at their locations.
• There are 4 different cats in the paper airplanes.
• The Extras section is for any moving things I didn't capture on previous screenshots.

Quality is a bit low on some of the images, nothing major, I had to adjust it to fit the size limit for the guide.
Happy gaming!