Board Thread:General Discussion/@comment-31981697-20170722123329/@comment-32182236-20170801012636

Alright, I think I get the quote you mean. "She holws, like it's the best joke she's heard in a hundred years". First, Sans says it's LIKE it's the best she's heard in a hundred years. Second, the other humans could have told Toriel jokes before also. Third, we don't know how long ago Sans started making jokes with Toriel. In fact, the promise could have been made as early as directly after the third human died. (Asgore getting his second SOUL)