When I took differential equations there was an article in my book about chaos theory which had nothing to do with diff. eq., but broke up the monotony of class pretty well.
The article was something like this:
Imagine you have a machine, similar looking to a compass, with a needle and degrees marked. Every second the machine doubles the angle between the needle and the zero degree mark.
You set the needle to whatever angle you want, and let the machine run for 30 seconds (30 angle doublings). It wouldn't be too incredibly difficult to predict where the needle would be at the end of the trial.
Now, suppose that after you set the angle, but before you turn the machine on, that ******* meddling butterfly comes along with it's flapping wings creating turbulence and mucking everything up. Suppose it perturbs the needle by one billionth of a turn (360/1,000,000,000 degrees). Now we set the machine in motion. In the first turn the one billionth of a turn error becomes doubled, then quadrupled, etc, so that after 30 seconds the error is 2^30/1,000,000,000 or 1,073,741,824/1,000,000,000 which is greater than one turn. We would have no way of predicting where the needle would be.