one may smile, and smile, and be a villain

The scientists say they know how it works;

 Psychopaths do not lack empathy, rather they can switch it on at will, according to new research.

Placed in a brain scanner, psychopathic criminals watched videos of one person hurting another and were asked to empathise with the individual in pain.

Only when asked to imagine how the pain receiver felt did the area of the brain related to pain light up.

Scientists, reporting in Brain, say their research explains how psychopaths can be both callous and charming. 

Like politicians.