In a falling dominoes model of nuclear fission chain reaction, what does the standing dominoes represent and what do the fall of the dominoes represent?

The standing dominos would represent nornal atoms that haven't been struck by electrons. The fall of dominos would represent an atom being hit by an electron sending out electrons to make more atoms split. Thus making a sort of domino effect.

I’m guessing you’re more alert to yourself or your surroundings if you’re more concentrated