Guess why they are alike. They all sing. They all sing in much the same way, too.

Watch very close and find out how you sing. You fill your lungs with air. Then you nearly close your throat and force the air out through a small opening. As the air goes out, it presses on the cords in your voice box and sets them to trembling, or vibrating like violin strings. A bird sings in the same way. Now watch the kettle. The kettle is full of water and air. Don't forget the air. When the water begins to boil it turns into vapor, or water gas, by exploding into bubbles. Vapor needs more room than water. So the first thing the vapor in the kettle does is to force the air out through the spout of the kettle. That is just like the narrow opening in your throat. Then the vapor keeps coming out in such rapid little explosions that the kettle vibrates. That makes the singing. Sometimes it "sings," or vibrates, so forcibly, that the lid of the kettle dances, keeping time like castanets.