4. KPD patients may suffer from a form of humor impairment. They frequently report that they have difficulty understanding what is humorous about some jokes that others find amusing, particularly word-plays. One case report noted that, asked to give an example, a patient said, "What has four wheels and it flies?" instead of, "What has four wheels and flies?" The answer to the former might be, for example, "a Cessna" (a brand of airplane; thus, this is an answer without humor) and the answer to the latter is "a garbage truck", but the KPD sufferer could not understand the difference between the two questions and why one might be amusing and the other not.
