What do you do with the broken shards of an item that was (or wasn't) designated before Shabbat? The daf follows the process of argumentation that emerges on this discussion. Side-point: A paradigm of impurity. Also: A contraption that involves filling it up on Shabbat -- and introducing the "basis" category of muktzah, depending on your intent. But how can you tell what happened how?! And the daf offers the same structure of argumentation as above, and that familiarity helps us understand the less familiar cases. Plus: Did R. Yehudah HaNasi require an action to pull something out of muktzah status, or is designating alone sufficient? Recommended: Point by Point Daf.