In the Friends season 4 poster, we see all of them sleeping:

[![enter image description here][1]][1]

While all of them have closed eyes, Rachel kept them open. There are various conspiracies about it like it's [all a dream](http://www.dailymail.co.uk/femail/article-4682788/Friends-fan-theory-Rachel-s-dream.html).

But is there any legit reason for it?

  [1]: https://i.sstatic.net/qQONT.jpg