At least three things indicate that the fog is similar like a cat. The fog begins gently and quietly, like a cat. The cat then rests on its haunches and looks about. Finally, it flees like a cat. As it does so, it hisses. Fog is mostly water vapor that has been cooled by cold air moving over land or water. As this cool air passes over warmer objects it will release some of its heat through evaporative cooling. This is why it is common for there to be less moisture in the air during periods of high wind speed or rain. Fog is usually not dangerous, but it can cause accidents if you do not see clearly. If you are driving in foggy conditions, stay aware of your surroundings and allow more time to reach your destination.