"Tumbleweed rolling across the room/blowing across the screen"

Henry : thanx for your prompt reply. but I would like to know what it means when someone responds to something you said with "tumbleweed roling across the room".

what is the meaning to this expression? thanks in advance

It's a Hollywood symbol of the Wild West.
www.abc.net.au/science/k2/trek/4wd/Over69.htm
Tumbleweed; Whenever you think of the Wild West of America, you think of cowboy movies and tumbleweed, perpetually tumbling around a desolate landscape. According to the American movies, tumbleweed is as American as apple pie. But tumbleweed is not a native American. It's a Russian invader, that was first discovered in Australia.
On our recent trip through Central Australia, we saw lots of tumbleweed. Occasionally, with a good tailwind, the tumbleweed moved faster than we did! The tumbleweed is a rather peculiar plant, because it actually moves around - it does not spend its whole life stuck in the soil. Once its seeds are ripe, a layer of cells in the stem of the plant weaken, and it breaks cleanly away. At this stage, the tumbleweed is almost a perfect ball with about 250,000 seeds stored inside. The wind then takes control of the tumbleweed. The ball is designed so that when the plant hits the ground as it tumbles along, it bounces and it won't lose all of its valuable seeds in just a single bounce.