A college professor of mine told me that a neuron firing is like flushing a toilet. I can't remember all the similarities, but I know that one related to the refractory period. Once you flush a toilet, you can't flush it again right away, and a neuron can't fire twice in rapid succession, either.
Some other similarities were that both are all or none (you can't half flush a toilet, and a neuron can't half fire) and both go in only one direction (fortunately, in the case of a toilet!).