Example: In pairs of two, students create a presentation about the achievements of the Roman Empire. They find 20 interesting images and explain to the class how Rome influenced our world and still impacts us today in five minutes (no text). This means students must prepare in advance and make a point and visual impact. Note: at this time google slides does not have an auto advance feature but Powerpoint does. This keeps kids exactly on 20 seconds each slide.
Check this website out to show you tons of examples and how it works.