Terminal lucidity is when gravely ill people have a sudden and unexpected moment of mental clarity. This seemingly impossible phenomenon has been seen in people with dementia, tumors, neurological disorders, and many other forms of brain-ravaging illness. The ability for the brain to - even temporarily - return to mental clarity calls into question scientists' models of what is actually going on in the brain. Understanding the phenomenon more could lead to improved caregiving practices and also a new understanding of the nature of dementia.