Some characters feel a current line of discussion is really inappropriate, and they make it clear they should move on to something else. Sometimes they say "moving on", or just leap into another topic. Reasons the current subject isn't working can vary. Either it's Squick, Too Soon, or even something like a Metaphorgotten line. There's a hand gesture that shows up frequently in Anime and Manga, that means basically this. Compare Stunned Silence, Shutting Up Now. Contrast Digging Yourself Deeper (trying to talk your way out of an uncomfortable subject, and utterly failing).