The two pictures above are photos of a Fish Basin made in the Ming Period of China (about 400 years ago). A fish basin a basin with four fishes curved on it, which is used to contain water or wash things just like normal basins. But what is special, it has two handles. When you are rubbing the handles with clean hands slowly, it will give out a low strong sound, and slowly, the curved fishes on the bottom of the basin start to "vomit" water!
Of course, the fishes do not really vomit water. But how did they do that?
The basin is made of copper, and its ply is about 0.5cm. It can vibrate mightily. When we rub it, we are giving it energy. If we rub it with a specific frequency, sympathetic vibration engenders, so great wave is formed. But the basin is put on the table. So the wave is standing wave. The swing usually has four points to reach its extreme value. They are just where the four fishes are. So water vibrate more and more mightily, then slop out of the basin.
If you want to try yourself, you can come to Chinese Science Museum.