Pratt refers to an obscure diagnosis as a "zebra". This is a reference to a popular medical school adage about considering common diagnoses before considering obscure ones: "When you hear hoof-beats behind you, think horses, not zebras." (The saying originated with Dr. Theodore Woodward at the University of Maryland, who originally said simply, "Don't look for zebras on Greene Street," referring to the street in Baltimore where the University of Maryland Medical Center is.)
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