Presenter notes: Open by reminding the class what worked last lesson and then breaking it. Every shape gave in to a pair of scissors: cut it, slide the piece round, and it became a rectangle. Hold up a paper circle and ask where they would cut. There are no straight edges, so there is nowhere obvious to start. Let the difficulty sit for a moment before you say that the trick still works, it just needs a lot more cuts, and that today they will cut a circle into a rectangle with their own hands.