https://www.reddit.com/r/explainlikeimfive/comments/3pni12/eli5_what_would_our_vision_be_like_if_we_had_a/ What would our vision be like if we had a third eye at the back of our head? https://en.wikipedia.org/wiki/Email_loop If one such automatic response triggers another automatic response on the other side, an email loop is created. https://en.wikipedia.org/wiki/Molyneux%27s_problem “if a man born blind can feel the differences between shapes such as spheres and cubes, […]