Board Thread:General Discussion/@comment-26242189-20160623232543/@comment-27701762-20160627222319

Perhaps it is simply a case of dramatic framing: time appears to stop so that A) the player is focused on a specific thing, and B) the seriousness of the plot element is not diminished by tiny details such as blinking or other movements. You certainly see similar ploys in television and movies, especially in the form of "time slows to a crawl while a character looks around quickly and processes enormous amounts of information," but it doesn't mean that the character literally slows down or stops time.

Especially since attributing such amazing powers to both Sans and Flowey completely messes up everything the game tells us about how they and the world work.