Board Thread:General Discussion/@comment-32182236-20190716003715/@comment-33883848-20190808115151

About Sans's comment about turns,you can actually attack him when he fall asleep despite the fact that he he didn't attack you first,so i think that it a kind of "politeness"rule or something.HOWEVER,it's heavily implied that Undertale is either canonicaly a game or work one because of this line:

"At least we're better than those sickos that stand around and WATCH it happen... Those pathetic people that want to see it, but are too weak to do it themselves. I bet someone like that's watching right now, aren't they...?"

Flowey is clearly referring to people who watch let plays and think that "someone like that is watching right now"which is obviously a reference to the player.There's a lot of instances like that endorces this theory,notably Alphys's belief that someone out there is watching,sans who always turn in the direction of the forth wall ,etc....