The process of making a diagnosis is integral to the practice of medicine, but diagnostic reasoning is rarely taught as a specific point. In most instances, experienced clinicians use a method of generating and testing hypotheses, finally selecting the hypothesis that best explains the clinical picture. Occasionally, especially distinctive physical signs allow augenblickdiagnose, a term that means "diagnosis in the blink of an eye." The process is too rapid to have followed a hypothesis testing method. Similarly, key fragments of history often permit very rapid diagnosis. The ability to make a snap diagnosis based on characteristic physical signs or snippets of clinical information relies on familiarity with certain critical clinical information. The reader is invited to try to augenblickdiagnose several cases.