The sound of feet on snow is an example of the stick-slip phenomenon. Other examples are squealing tyres and violin music. When you try to drag one object over another the friction between them prevents movement. The objects won't move at all until the dragging force at least matches the friction force. However, if they are elastic (and everything is a bit elastic), they will stretch. Then, when the elastic force matches the friction force, sliding starts. For most materials, the friction force is higher when they are not moving than when they are. When movement starts, the friction force drops and the stretched elastic force will suddenly be too big, so the dragged object will accelerate as the stretch contracts.
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