When the temperature drops to near zero degrees Celsius, if there are small droplets of super-cooled water in the atmosphere. When these droplets touch the surface of an object, they suddenly transform into ice with fine structure, soft and easy to fall off. Fog will have various shape depends on the object they attached. Because the "saturated water pressure is lower" at the tip or corner of the object, the fog is easy to accumulate there. (Rime has two types: hard and soft).