Differentials are very difficult to explain to someone and even though we've messed with them for years, it's still a complicated feat of engineering to comprehend.  The funny thing is, that even with today's computer animations, the video below (from 1937) is probably the best one we've ever seen.  Despite Chevrolet's back-turn to safety procedures (helmets anyone?), they did a super job.   Hat tip to Jalopnik.com for turning us on to this video.