Why is this the answer?

The answer is frost because this clever riddle uses fun words to describe something very cold and sparkling that you often see in the wintertime. It asks you to think about what happens outside when the weather gets super chilly. Let us look closely at the first part of the riddle: "Goes over all the hills and hollows." Imagine waking up on a very cold morning and looking out your window. What do you see? The entire world might look like it is covered in a soft, bright white, glittery blanket. That white blanket is the frost. Frost is made up of tiny little ice crystals that form when the temperature drops low enough. These tiny crystals do not need a road or a path to travel. They do not need a car or a bus. Instead, the frost spreads out wherever the cold air goes. It can easily cover the very tops of the big hills and also go down deep into all the little hollows, which are the low places or valleys in the ground. It covers every blade of grass, every branch, and every surface outside in an even way, almost like a giant painter covered the landscape with a brilliant, temporary white coat. This part of the riddle helps you picture how frost appears everywhere, without missing any spot, when the air is truly cold. Now let us think about the second part: "Bites hard, but never swallows." When we say the weather "bites," what we mean is that the air feels super cold and sharp. Have you ever stepped outside on a freezing day and forgotten your gloves? The cold air on your fingers feels sudden and almost painful, like a little pinch or a "bite." That is the cold biting you. Frost is very, very cold. When you touch it, or when it settles on plants and leaves, the sharp coldness makes it feel very hard. The word "bites" is a way of saying that frost is strong and makes the world feel extremely cold and solid, even hurting things like delicate flowers or fruits. But, of course, frost is not alive and cannot actually eat anything or truly "swallow" it with a mouth. It just freezes things solid. So, the riddle is asking you to think of something that spreads across the entire landscape and feels sharply cold, like a bite, but is not a creature that can eat. That mysterious and beautiful white covering that comes with the freezing temperatures is the perfect answer: frost.