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A 58-year-old man with a 10-year history of idiopathic Parkinson's disease presented with an incapacitating freezing of gait (Panel A, Video 1). The patient had severe difficulties initiating gait and was able to take only a few shuffling steps when provided with a visual cue (the examiner's foot placed in front of the patient). Attempts to walk evolved rapidly into forward festination and ultimately a fall to the ground. Axial turning was impossible. However, the patient's ability to ride a bicycle was remarkably preserved (Panel B, Video 2). Gait freezing recurred instantaneously after he dismounted the bicycle. This striking kinesia . . .