One time when I was called up for jury duty the pool was asked whether any of us had heard of jury nullification. I raised my hand and the lawyer (I think it was the prosecutor but it might have been the defense attorney) asked what I knew about it. I gave a long enough answer that he made a smartass comment that maybe I was on the wrong side of the rail. I wasn't invited back for the actual trial even though I started in the top 12.
I've heard that the whole voir dire process was started before the Civil War to locate and remove jurors who were abolitionists on fugitive slave law trials because they had a tendency to vote not guilty no matter what the facts were.