It was the sort of incident that happens at facilities that care for people with dementia . At a residence for older adults in San Francisco last summer, Carol King momentarily left a common sitting area. When Ms. King returned, she found that another resident had taken her chair, a nurse who witnessed the episode later reported. She grabbed the usurper’s wrist. Though staff members intervened promptly and nobody appeared injured, the other resident (who also had dementia) called 911 to say...