Board Thread:General Discussion/@comment-27414715-20160302213117/@comment-26347196-20160303215018

After befriending Undyne, when you call Papyrus, he sees Undyne as she is panting. While Papyrus did not mention Sans teleporting, he does mention Sans having "shortcuts".

But, I won't confuse you anymore and I'll stick to one fact. When Undyne is panting, it indicates that she ran, because you don't see Sans panting at all when he teleports.