Why is this the answer?

The answer is wood because this is a very clever riddle that makes you think about how a piece of wood lives its life, even after it is cut down from a tree. This puzzle uses creative clues that point to the amazing and useful things we get from trees. Let us look at each clue to see why wood is the perfect answer. The first line is a bit tricky: "I am the heart that does not beat." Did you know that the center part of a tree trunk is called the heartwood? It is the strong part of the tree, just like your heart is the strong center of your body. But a tree's heartwood is not alive anymore, so it does not beat like a human heart. That is why this clue fits so well. Next, the riddle says, "If cut, I bleed without blood." When a person cuts into a living tree or even a fresh piece of wood, a thick, sticky liquid called sap comes out. It can look a little like a cut is bleeding, especially the reddish sap from certain trees, but it is just the tree's own special food and water, not real blood. The third clue is about flying: "I can fly, but have no wings." While wood cannot fly by itself, people use wood to build many things that soar high up in the air. Think about a simple kite! It has a wooden frame, and it flies with the wind. Long ago, the first airplanes were also built mostly from strong, light wood before we had metal planes. So, wood is the secret ingredient for many flying things. Then the riddle tells us, "I can float, but have no fins." This is a fun and easy one! If you put a piece of wood, like a fallen branch or a log, into a lake or a river, it will float right on top. It does not need fins like a fish, or an engine like a boat, because wood is naturally lighter than water. Finally, the riddle says, "I can sing, but have no mouth." Wood is a champion at making music. Many musical instruments, like guitars, violins, clarinets, and pianos, are made from wood. When a musician plays them, the strong, hollow wood vibrates to make wonderful, clear sounds. The wood itself is the part that sings, even though it does not have a mouth to speak or sing a song. Wood fits every single one of these amazing clues!