He gives a wonderful comparison between the fog and a kitten. When a kitten comes around us, most of the time it just comes so slowly that you hardly notice, till you see it or feel it. The same is the case with the fog. An arrival of fogs cannot be predicted. It just comes in and engulfs the entire place that it is and stays on for some time, creating trouble for anyone in between it, but still stays as though it is not aware of the happenings around it.
The next four lines of the poem states that it just comes, sit at the harbor and looks at the city and is at the silent haunches and then finally moves on. Here the poet has described what happens once the fog has arrived.
Now, Fogs as such do not cause any harm, as it is silent and the onset is slow. However, when the fog is around, especially in the city, many accidents may occur for the only reason that people cannot see anything in-between them. There are occasions, when people fall into telephone holes, cars may hit onto each other. People may walk up the wrong place, at the harbor, boats may drive up on the wrong bridges, or they may drive up on another boat and many such instances. Therefore, a fog just comes in like a small and silent kitten, and just sits and watches the beauty, but when it is over a city, the incidents caused by the fog are many.
And the last line states that , just a small child, who gets bored playing the same game over and over again or just by seeing the same sight again and again, and moves on to the next, similarly, the fog also does not stay in one place for a long time. After some time, after the pranks are over, the fog also moves on.
This is a very small poem describing the nature’s act in a beautiful manner.