Some patients' own hand acts on its own, against their will
After certain strokes or split-brain surgery, one hand can perform purposeful actions, unbuttoning a shirt the other hand just buttoned, grabbing objects, even reaching for a partner's throat, while the patient insists it doesn't feel like their own and can't be consciously controlled. The condition was first clearly described in 1908 and named 'alien hand' in 1972.