"Mweh Heh Heh!" is the 16th track in the Underswap Soundtrack. It is an upbeat song with an 8-bit sound. In addition to being Sans's theme music, this track is part of an easter egg that plays at the end of a Pacifist Run of the demo, playing during and after Sans and Papyrus' conversations. There have also been some hints of this song playing during Sans's battle.
Team Switched Differences
It is known as "A real sansation" in Team Switched's fangame.