Cute joke about knowing vs believing

[MadMonk]

Mr. Bahr was convinced he was a mouse. He was finally institutionalized. After about 2 years of treatment, Dr. Hackenholt checked up on him to see how his treatment was progressing. Mr. Bahr assured the Dr. that he no longer thought he was a mouse. The Good Dr. assured Mr. Bahr that if he really did not think he was a mouse anymore, that he could go home. After several days of evaluation, Dr. Hackenholt determined that Mr. Bahr could go home. On the way out, the Dr. asked Mr. Bahr if he had any questions. Mr. Bahr replied "Yes Doctor, I do have one question. I am sure that I am not a mouse but, do the cats on the street know this?"