They probably use the trick where they blow air in the sand to give it "liquid" properties where they need the sand to flow. For those who haven't seen it ther

They probably use the trick where they blow air in the sand to give it "liquid" properties where they need the sand to flow. For those who haven't seen it there is a famous Mark Rober video: https://www.youtube.com/watch?v=My4RA5I0FKs https://www.youtube.com/watch?v=My4RA5I0FKs