Paper-Folding an Ellipse
Start with a circle drawn on paper and mark a point inside it. Fold the circle so that the circumference touches the point. Make a firm crease. Repeat, using random folds. The creases form the envelope of an ellipse.
The locator represents the point inside the circle. You can move the locator and vary the number of creases.
 D. Wells, The Penguin Dictionary of Curious and Interesting Geometry, London: Penguin, 1991.