"Oh..." They pause for a moment, picturing it. "Okay. That's unusual, but it also makes sense."

"Monster souls are made of compassion and love," they explain. "Mercy is important to them. If he wasn't trying to kill you, then he probably didn't want to risk that getting worse." They point at his injury again.

It's possible that Sans just didn't want another mess to be harassed over, but... No. Even when pushed to their most extreme, monsters didn't usually attack willy-nilly. Sans even moreso: it took an impending apocalypse just to rouse him from inaction. Why had he attacked this time? Maybe he was trying to be proactive for once in his slug-like life. One violent human was bad enough, after all, so wouldn't he worry more about two?