If this ever happens to you, make sure that you answer with complete sincerity and as relaxed as possible. It's useless to ask the interviewer what the question is about or to beg for an explanation.
Most of the times it's only to measure your skills to deal with strange situations or to know what your behaviour is like from a psychological point of view.
There can be of many types of questions, such as what kind of march you would organize against the company you are applying to ( this is used to know if you see something negative in the company);or questions testing your general knowledge such as: "What amount of pizza was eaten in the USA last year?" ( you don't have to know the answer; it is only asked to know if you have any problem in saying "no" and being sincere with the person that in the near future may become your boss).
Here there are some more examples of weird questions asked in job interviews from well known companies:
1."How lucky you are and why?" - Airbnb
2."If you where a pizza delivery man how you would benefit from scissors?"- Apple
3."If you could sing a song in American Idol, what song would it be?"- Red Frog Events
4."Do you believe in Big Foot?"- Norwegian Cruise Line
5."Why is a tennis ball fuzzy?"- Xerox
6. "If you were 80 years old, what you would say to your grand-children?"-McKinsey & Company
7. "If you are a new addition in a crayon box, what colour would you be an why?"- Urban Outfitters
8. "Describe to me the process and benefits of wearing a seatbelt"- Active Network
9. "How does the internet work?"- Akamai
10."If you were on an desert island alone, what three things would you bring with you and why?"- Yahoo
11. "What is your least favourite thing of humanity?"- ZocDoc
12. "If you were a box of cereal, what you would be and why?"- Bed Bath & Beyond
Here is an example of a very simple question to get a job as a salesman or a broker. It shows how difficult it is to give an intelligent reply when the answer is totally obvious.