How to catch flies off the ceiling in Kurt Vonnegut’s “God bless you Mr Rosewater”.

Take a tall drinking glass and put in dish soap. Fill with water such that the foam extends above the top of the glass. Slowly raise the glass up under the fly. The fly drops from the ceiling and turns over to actually begin flying. By the time the foam is close and visible the drop is close enough that the fly gets caught in the foam, sinks to the water below and then drowns.

And yes I’ve tried it