A notorious smuggler was caught because he mailed a letter with a stamp placed upside down on the envelope. The postal inspector laughed, saying the smuggler did it on purpose to send a secret code. The detective shook his head, saying it was just sheer carelessness. How did the detective know?
A machine cancelled it
Modern postal sorting and cancelling machines automatically stamp the postmark correctly regardless of how the envelope is oriented. The upside-down stamp meant it was handled by a human or poorly inspected.
About this riddle
Detective riddles are tiny mysteries. Look for the detail in the story that does not fit; it is usually the clue that solves the case.
Difficulty: Hard. More like this: Detective riddles with answers or try Truth & Lie Island for a different kind of puzzle.
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