Finally a chance to sit down and feel things instead of shoving it all down to face crisis after crisis, haha. Able now to look back at what happened to them with full understanding! Poor Sans in particular needed this - hes never really owned or acknowledged any of the suffering he personally went through. Hes always put Papyrus first and he still does to this day, even when it hurts him. He blames himself for when Papyrus got hurt back in the lab, even though the only one responsible for that pain was Gaster, and as a result he never focuses on anything that happened to him, only to Papyrus. On some level he feels like he deserved it while Papyrus didn't, or at least he deserved it more. So hearing someone acknowledge that HE also suffered and his pain is legitimate and deserving of sadness is a bit overwhelming for him. Although theyre both kind of overwhelmed right now, haha.

This kind of thing can be so complicated! Thus Sans's conflicted feelings and confusion about how to deal with them. There isnt really any way to prepare for dealing with something like this... much less any kind of guide.

Edit - OOPS FORGOT GASTER'S ARM IT'S BACK NOW