He remembers the kid's first name, but the last one escaped him. Good to have a face to put to the name anyway. Candlelight ain't exactly the best way of pickin' up people's facial features, and humans all kinda look the same to him.

"Might wanna watch what you call 'monster'," says Sans, the words little more than a pleasant rumble. "Technically, I'm classifiable as exactly that."

Even if he apparently has moral quandaries with killing the things in the Colosseum. That'd make him in the minority.