The most objective and complete summary is:
"The story is a fable about a cat who tries to show its animal friends a picture. The friends all make the mistake of standing between a mirror and the picture, so they only see themselves—not the picture. Because they all see something different, they each mistakenly think the others are lying. In the end, they are all angry with each other and the cat is the only one who understands what happened."
This summary provides a clear and comprehensive overview of the main events, the conflict among the characters, and the outcome, while also mentioning the moral of the story.