Various interesting cases in conjunction with weighing on Shabbos.
Moving a Candelabra That Has Oil in It on Shabbos. Using a Dimmer on a Light on Shabbos;
Automatic Toilet Flushers, Automatic Sinks, Soap Dispensers, Doors, etc.
opening Up a Loose Leaf, "My Key Is Bent, Could I Bend It Back in Shape?", and Fixing a Safety Pin;