Why is this the answer?

The answer is needle because this clever riddle uses fun word pictures to describe an object that helps us fix clothes and make beautiful crafts! This little puzzle has three main clues that fit perfectly with a sewing needle and the thread that goes along with it. First, let's look closely at "An iron horse." The needle itself is a small, strong tool made out of metal, which the riddle cleverly calls "iron." When a grown up or even a kid is sewing, the needle moves very quickly back and forth. It’s going up and down through the cloth, pulling the thread with it. Because it moves so fast and is made of strong metal, the riddle calls it a speedy "horse." This is a wonderful example of how riddles make something tiny and common seem big and important with imaginative language. The next clue is "with a flaxen tail." This part describes the long piece of thread that you push through the tiny hole, which is called the eye, at the end of the needle. A long, long time ago, thread was often made from a plant called flax. Even though the thread we use today might be made of cotton, wool, or other materials, the riddle uses the word "flaxen" to describe the color and material of the thread. This thread is the needle's "tail" because it follows right behind the sharp point, just like a tail follows a horse. Finally, we have the last part: "The faster the horse runs, the shorter his tail becomes." Imagine you are sewing a patch onto your favorite toy. The more stitches you make, the more thread the needle pulls through the fabric. The "horse" (the needle) is running fast by doing a lot of sewing, and as it moves, it uses up the thread. The amount of thread left on the spool or left trailing behind the needle gets shorter and shorter the longer you keep going. This shows you that the faster you work, the quicker the thread "tail" disappears! It’s a fantastic riddle that helps us see a simple, helpful tool in a brand new, imaginative way, teaching us a little bit about history and sewing all at once.