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You visit a remote desert island inhabited by one hundred very friendly dragons, all of whom have green eyes. They haven't seen a human for many centuries and are very excited about your visit. They show you around their island and tell you all about their dragon way of life (dragons can talk, of course).

They seem to be quite normal, as far as dragons go, but then you find out something rather odd. They have a rule on the island which states that if a dragon ever finds out that he/she has green eyes, then at precisely midnight on the day of this discovery, he/she must relinquish all dragon powers and transform into a long-tailed sparrow. However, there are no mirrors on the island, and they never talk about eye color, so the dragons have been living in blissful ignorance throughout the ages.

Upon your departure, all the dragons get together to see you off, and in a tearful farewell you thank them for being such hospitable dragons. Then you decide to tell them something that they all already know (for each can see the colors of the eyes of the other dragons). You tell them all that at least one of them has green eyes. Then you leave, not thinking of the consequences (if any). Assuming that the dragons are (of course) infallibly logical, what happens?

If something interesting does happen, what exactly is the new information that you gave the dragons?

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marked as duplicate by f'', Jonathan Allan, Marius, Hugh Meyers, Aza Aug 3 '16 at 7:06

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    $\begingroup$ do we have a tag for green-eyes problems, or should we misguidingly tag this as blue-eyes? :) $\endgroup$ – elias Aug 3 '16 at 6:44
  • $\begingroup$ This is just the famous blue-eyed puzzle replaced with green eyes... Pretty sure someone would flag this as duplicate $\endgroup$ – Sid Aug 3 '16 at 6:44
  • $\begingroup$ its even on the right, in related posts lol $\endgroup$ – lois6b Aug 3 '16 at 6:46
  • $\begingroup$ Shouldn't the puzzle specify that the dragons all know that they are all infallibly logical? $\endgroup$ – Brent Hackers Aug 3 '16 at 6:55
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    $\begingroup$ I would suggest not down voting. It's a good question and it's not obvious to newcomers how to search for duplicates. Closing a question doesn't mean it's bad, it's just the stackexchange way of trying to keep all the useful discussion on a particular question in one place. Welcome to stackexchange, Boris. Keep asking questions! $\endgroup$ – Hugh Meyers Aug 3 '16 at 7:10