Metaphorical semantic extension takes place in the course of radiation, while metonymical semantic extension takes place in the course of concatenation.
He himself, facing a firing squad, would not understand too well the concatenation of the series of subtle but irrevocable accidents that brought him to that point.
For example, many programming languages have a string concatenation function, or " strcat" , which takes in two strings, and copies the second one to the end of the first.