He is seen throughout the game following the human around, so long as Papyrus is not killed. Sans quits following the human if they kill Papyrus, after all, which shows there is some personal emotional investment in him for following the human around and interacting with them all the way to the CORE.

Why does Sans kill you if you spare?

It seems like getting dunked on after sparing Sans is a complete suprise, but he actually quite explicitly warns you that youre going to die if you SPARE him. His exact words are Youll make my job a lot easier. So his job is killing you.

Can Sans kill a human?

We dont know when Sans made his Dont hurt humans promise. It could very well be after a few of the humans that fell down died. With this in mind, Sans may have fought Orange and killed him, as his blue attacks counter movement.

Is Sans aware of Flowey?

So, there you are: Sans doesnt know about Flowey, so he assumes you to be responsible for his actions.

Can Sans beat Flowey?

Thus, Sans has killed Flowey many times and because of this Flowey gave up after awhile. There is the theory that Sans was, or is, a human, and that would explain why he had caused Flowey his fair share of resets. Because Sans is already powerful as a monster, and as a human, he would be unstoppable.

Can you call Toriel after leaving the ruins?

The player cannot call Toriel once they exit the Ruins even if she was spared. While most players may assume that Toriel intentionally refuses to answer the protagonists calls outside of the Ruins, she is actually unable to answer due to the Annoying Dog having stolen her phone.

What happened to Sans eye?

When Sans uses telekinesis, his left eye flashes light blue and yellow, the colors for patience and justice, and his right pupil disappears.

Is sans the only one that can dodge?

He can dodge, I think because of determination. He only has one HP. That means even a single punch can take him down. However, we see that a fellow monster, undyne, has determination.

Why is Flowey afraid of Sans?

There is the theory that Sans was, or is, a human, and that would explain why he had caused Flowey his fair share of resets. Because Sans is already powerful as a monster, and as a human, he would be unstoppable.