Board Thread:Fun and Games/@comment-27524978-20160317154321/@comment-27620479-20160520142559

Sans doesn't necessarily know exactly what happened either. He doesn't even need to lighten it, Papyrus is known to outright ignore what he doesn't want to acknowledge anyway. Sans usually talks about disappearances and not explicitly deaths in his phone call "reports" to the protagonist. He realizes that it is their doing, but as far as I know, only explicitly calls them out on being dirty killers for slaying Papyrus.