Trees and Mines
RAY: The reason has to do with the sound certain woods make when they're nearing their break point. Many stronger woods would give no noise before the point of giving out -- cracking and breaking at the same instant. But poplar will begin to break at the point it begins to strain or stretch, making loud cracking noises. When this would happen, you'd hear the following noises if you listened carefully: "Get out of here!!"
[ Car Talk Puzzler ]