Dishonored secrets and facts. {Spoilers}

Some of us did not play the game in different ways, some of us did not get all the endings, some of us went quickly through the game leaving much secrets undiscovered, here, we would like everybody to share with us those small but interesting facts that they came across while playing Dishonored (+Dlcs), what do you know that we don't?, share bellow.

Note : this post is tagged spoilers, so please don't tag your comments and submit whatever information or spoilers you want.

Note 2 : Thank you all for all the tips and facts, i hope this post becomes helpful to some people as it was for me.