Ok so I probably can't call it a 'fact' because I'm not Toby Fox, but I always love putting "Fun fact!" before a slightly dark statement that's not exactly fun in any sense of the word.OK!! SO!! Let me explain this because you guys know me. I never just say something about a character if I don't have a reason to.If you haven't played the game at all and still want to I'm probably gonna mention some things you might prefer finding out yourself when you play the game. Just a heads up.Sans asks you to join him at Grillby's for a burger or fries immediately after you first leave Snowdin. What follows is a rather strange conversation, but in retrospect it actually says a lot about Sans' character. The scene happens after you leave Snowdin, which is also after you've befriended Papyrus. Now I haven't tried every path in the game but if you go directly back to Snowdin and speak to Papyrus you have your hang-out session in his house... where Sans also is at the time.Back at Grillby's, the first thing Sans asks you is what you're opinion is of Papyrus... even though he knows you've just made friends with him and saw the two of you hanging out in his house. He still asks you face to face what exactly you think of Papyrus. Basically, he's trying to get a gauge of how trustworthy you are.Secondly, he brings up the talking flower. He mentions that Papyrus has told him that he's been speaking to a talking flower that's been whispering things to him like advice, encouragement and predictions. Sans says he believes it to be some kind of trick being played on Papyrus. He then says to "keep an eye out" for it... even though nothing hes mentioned would suggest that the flower would be any threat to YOU. We as the player have an idea of who the flower is... but Sans doesn't know this.Basically, he brings it up to see Frisk's reaction. He's trying to figure out if Frisk has anything to do with the talking flower, but he doesn't want to just outright blame you for no reason.Basically.... it's a veiled threat. "You're a human walking around the Underground and weird things are happening. I dunno if you're involved, but don't fuck with my brother. Because I'm not stupid and I notice things."Lastly, he breaks the tension and reverts to being more laid-back and relaxed. Before he leaves the diner though, he mentions he "was going to say something but forgot what it was."Chances are he was going to mention that if it wasn't for the fact that he made a promise, he would absolutely have killed you the second he saw you. But he decides against bringing it up because this is still early in the game, and he's still trying to figure you out. So he holds off n mentioning it until later in the game.So... why bring any of this up?Because you befriended Papyrus.Before that you were just kinda this weird human who had to be kept an eye on. Sans speaks to you and jokes around with you and mentions that it'd probably make Papyrus happy toa human. But after you actually become FRIENDS with Papyrus... you become a more personal danger. So Sans asks you to get a burger with him so he can size you up a little bit, and decide whether he shouldn't just end you after all.or at least that's how I understood things.