Board Thread:General Discussion/@comment-27136653-20180228205701/@comment-32182236-20180228220402

Believe it or not, I’m actually going with a. We actually know this for a FACT.

Undyne attacks you with her spear in her final encounter-That’s what begins the FIGHT in the first place. Nothing happens to you, other than that entering the fight. Same thing for running into her summoned spears.

So basically, monster attacks can’t directly harm the body. But they CAN force you to enter a FIGHT, where the SOUL can be harmed. And, since all of your determination is inside that SOUL, of the SOUL shatters, or is absorbed.. You can say bye-bye to having a living body.. But it’s not damaged, just dead due to a lack of DT.