What is the difference between 'continual' and 'continuous'?

The words continual and continuous are like twins: they both come from continue, but they get mad if you get them confused. Continual means start and stop, while continuous means never-ending. Continual is chronic, like a cough that comes and goes, or a teenager's sporadic fights with The Man. Continuous is like a circle, or a nightmare carousel that never ever stops. Neither one is the evil twin; they're both moody.