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 tearfulfarewell 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).
LOGICAL? Assuming that the dragons are (of course) infallibly logical, what happens? How many dragons, if any, become long-tailed sparrows and in what period of time?
PHILOSOPHICAL? While scratching your head, can you figure out what this logic problem has to do with polyamory? What might the dragons and sparrows represent, allegorically? What if the dragons are in a forest by themselves with a rock that God created so large and heavy that even God cannot move it?
CONSERVATION ECOLOGIST? Are you concerned more about the long-term survival and possible extinction of the green-eyed dragon in the wake of your very regrettable action? Perhaps if the dragons reproduced and kept the next generation from finding out about your careless reveal, the species can be saved.
SAPIO SEXUAL? Do you enjoy scrolling through the comments of intellectuals who attempted to solve this puzzle to see how their minds operate? Do you enjoy words like egalitarian and lascivious? Does learning turn you on?
ARTISTIC? What do the long-tailed sparrows look like while transforming from a dragon and in their final form? Sketch a scene. Sculpt a statue. Sing a song. Dance like no one’s watching, except that everyone is. But that’s okay.
The 100 Green Dragons logic problem originally appeared on io9 website with its solution where it was billed as either the hardest or the second-hardest logic problem in the world.