Why can't people see my cat?

One day I was in my room painting and I saw this cat on the window ledge. He was ginger and he had a top hat on and told me his name was Mr. Ginglebubble. And whenever I show him to people they always say 'There is no cat there...' And it really confuses me...why cant people see my cat. He's amazing. He dances and sometimes he sings musical numbers. Today he sang 'Roxie' From Chicago