These are sentences in which the latter part of the sentence or phrase is surprising or unexpected in a way that causes the reader or listener to re-frame or reinterpret the first part. It is frequently used for humorous or dramatic effect, sometimes producing an anticlimax.
I asked God for a bike, but I know God doesn't work that way. So I stole a bike and asked for forgiveness.
Do not argue with an idiot. He will drag you down to his level and beat you with experience.
I want to die peacefully in my sleep, like my grandfather; not screaming and yelling like the passengers in his car.
