Why is this the answer?

The answer is snail because this fun riddle paints a perfect picture of a small, quiet creature you might see creeping in your garden after a rain shower. It uses clever words to describe exactly how a snail moves and lives. Let us look at the first clue: "Who is he that runs without a leg." When we think of running, we usually picture fast things like a dog or a kid on the playground using their legs. But a snail is quite different. A snail does not have any legs at all! Instead, it moves along by gliding on its belly using one huge, strong muscle called a "foot." The snail pushes this foot out and ripples it, making the body slide forward very, very slowly. To help itself slide, the snail leaves a sparkly, wet trail behind it, which is the famous snail slime. Even though this movement is very slow to us, the riddle calls it "running" because the snail is certainly moving on its own from one place to another without stopping, just like a runner on a long, slow journey. Now, for the second clue: "And his house on his back." This is the key to solving the riddle! If you have ever seen a snail, you know that it carries a beautiful, swirly shell right on top of its soft body. This shell is the snail's home, and it is a very important part of the snail. It is hard and strong, like a little suit of armor that grows with the snail over time. The snail can tuck its whole body, head, and soft parts inside the shell any time it feels scared, tired, or when the sun gets too hot and dry. Since the snail always has its shell with it, it is truly carrying its home on its back all the time, which makes the snail the perfect answer to this wonderful, tricky riddle.