They’re figures of speech in which the latter part of a sentence or phrase is unexpected and frequently humorous. (Winston Churchill was a master of them, often with cutting effect.) Seven examples from all over:
1. Where there’s a will, I want to be in it.
2. If I agreed with you, then we’d both be wrong.
3. Knowledge is knowing a tomato is a fruit. Wisdom is knowing enough not to include one in a
4. To steal ideas from a person is plagiarism. To steal from many is research.
5. War doesn’t determine who’s right. Only who’s left.
6. We never really grow up. We just learn how to act in public.
6. You don’t need a parachute to skydive. You only need one to skydive twice.
7. To be assured of hitting the target, shoot first and call whatever you hit the target.
To spice up your fiction recipe, you may want to sprinkle in a few such small surprise twists of your own in sentence or paragraph form. They can be wry and subtle, and they work nicely when spoken by an unexpected character.