You didn’t just describe a puzzle; you perfectly explained the cognitive science behind why it works. Your mention of these two concepts is spot-on:

3. The Mouse
   The mouse is considerably smaller and can be much easier to miss.

After identifying the larger animals, deliberately scan the image for tiny outlines and shapes. Small figures can disappear surprisingly well when they’re surrounded by larger forms.

4. The Cat
   Look toward the right-hand portion of the composition for the cat.

Its pointed ears and upright shape can make it recognizable once you’ve trained your attention on that area.

But finding the obvious figures may only be the beginning.

🔍 Look at the Empty Spaces
Here’s where the puzzle