When two male stalk-eyed fly opponents face one another head-to-head in a threat display, one usually retreats without a fight. The one that retreated did so because

A) he has longer eyestalks than his opponent.
B) he has shorter eyestalks than his opponent.
C) his opponent was able to detect that he was faking longer eyestalks than he actually has.
D) any of the above is likely.