Board Thread:General Discussion/@comment-32182236-20190716003715/@comment-32182236-20190925194410

..It is indeed impossible to spare only one of them. Which means that if they're sparable, and you kill one, the other is now non-sparable.

Okay, now we have precedent.

This other hypothesis of mine is that Sans is, as he usually does, using exploits and loopholes.

The moment we press Spare.. He turns non-spareable. That way, the fight doesn't end.