How do you tell when a politician is lying?

John Key recently said that he will not reduce the number of bureaucrats via sacking; he'll rely on attrition to reduce the numbers.  Yeah right.

As The Standard notes, National has already promised to create 1000 more core public service jobs, all the while promising they would cap those numbers. And they haven’t identified a single one they would cut.

So how do you tell when a politician is lying?
Their lips move.