If a baseball player at bat swings and fouls a pitch off, he will frequently (in a wood bat league) turn the bat around end for end and tap the handle on the ground. Anyone who has played the game understands what he is doing. By the resulting vibration, he can tell if the bat is still sound or if he has broken it. I noticed a while ago, while sitting in one of my rockers, that if I tapped on one of the arms, the whole chair would vibrate. All my furniture seems to be that same way. The joints are so solid that the whole piece reacts like one piece of wood, like a solid baseball bat.