[Despite his own despair, Mettaton can sense Sans's too. It sticks out, something separate from his own trauma, and it catches his attention rather quickly. Unfortunately he can't really voice his concerns to Sans with the thick wad of fabric in his mouth so he merely yells through it, muffled and quiet, as Mirrorton retakes his stance and looks at Sans evenly.]

Ugh. What a disgusting thing to see on what is otherwise a beautiful day.

[He doesn't remember what Sans has done. To the memory, it is nothing. The end will always be fulfilled.]

No matter. You'll be easy enough to dispose of. Then I can continue doing what I need to do to keep my darling here with me. Forever.

[The memory will only end once Mirrorton's boots cross the threshold into the hallway. Therefore there is plenty of time for the encounter he is now activating.]