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Reader question: In this sentence – Researchers believe that the knock-on effect of people giving up smoking has been a major factor in the smoking decline over recent decades – what does “the knock-on effect” mean? My comments: We can perhaps best understand the knock-on effect by playing a game of domino bones. First we stand pieces of dominos known as bones up on end and side by side. Then we knock the first piece down toward the second one. If we space the bones correctly, the first bone will fall onto the second bone knocking the second one down. The second then, as it falls, knocks on the third, and knocks it down as well. The third, of course takes down the fourth in the same manner and the same thing happens over and over again ad infinitum. From this comes the term “domino effect”. Or, in other words, chain effect. Similarly, the knock-on effect refers to situations where one event leads to another. In the example from the top, when researchers attribute the decline in smoking to the knock-on effect of people quitting the fog, they mean to say that these quitters might have led to more people quitting the habit as friends and companions tend to influence one another. However, I must point out that the domino bones might not be a perfect analogy because the knock-on effect often refers to indirect influences one event has on another. Unlike the domino effect, which is direct or chain effect – events linking to others like a chain – the knock-on effect is not always readily predictable, as demonstrated by media examples below: | 
