What happens when an
event occurs that
triggers another event, which, in turn, triggers another event, which, in turn, triggers another even, which, in turn, triggers another event,
which, in turn, triggers another event, which, in turn, triggers another event, which, in turn, triggers another event...
Obviously, the phrase comes from domino rallies, in which odd hobbyists use massive piles of dominos all lined up so that the first one knocks down the second one, which knocks down the third, etc.