instruction:
Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.
question:
Double vision, the perception of two images from a single object, is properly called what?
answer:
double vision


question:
Mr Barkis, Edward Murdstone and Tommy Traddles are all characters in which Charles Dickens novel?
answer:
charles dickens


question:
Which Russian man designed the legendary AK-47 assault rifle?
answer:

ak-47