Answer:
What do you call the mother-in-law of your sister's husband?
What is it that you ought to keep after you have given it to someone else?
A blue man lives in the blue house. A red man lives in the red house. Who lives in the white house?
What can't you see, hear or feel, until it’s too late. What shadows love, and shopkeepers hate?
What is the center of gravity?
What is always coming but never arrives?