Chain reaction

Chain reaction is when one event causes another event, which causes another event and so on. It's like a snowball rolling down a hill. For example, when you drop a rock into a still pond, it creates a series of ripples in the water. Those ripples cause other ripples, like a chain reaction. So the rock being dropped is the first event, which causes a ripple in the water, and that ripple causes another ripple, and so on.