I Came up with that yesterday when i had a shower. So here it is. Imagine a fount(i am that the word for the found that throw water under us) in a shower that has a hole on the one side and hang on an ax that is set on the wall(inside the shower). The fount can turn easily right and left. So we make the fount to throw water under pressure. Now, we slap the waterfall with our hand. Is it possible debends the pressure of the waterfall to MOVE the fount slapping the water??Sorry for my terrible english.