Brain Test Level 22 There is an intruder in our cat party

Daze Puzzle provides a complete walkthrough for "Brain Test Level 22: There is an intruder in our cat party!".

By Daze Puzzle /
Question
There is an intruder in our cat party!
Hints
Hint 1:
You can spam clicking around.
Step 1
Answer
There is a hidden rat inside the red circle (look at the image above).