The case of a man nullifying a bill of divorce in the presence of the court, while a messenger was bringing the wife the get - he can't do this (she won't know about it!), but if he did it, does it count or not? The court's ability to decide whether his nullification takes effect seems dependent on kiddushin taking place with kesef, money, or an item of monetary value. The question of rabbinic power is very much in play. Plus, a series of examples of the rabbinic level of law, when in comes up against Torah-level laws. Including rabbinic corporal punishment (lashes) as serious enough punishment to protect people from violating Torah law. Plus, one who rode on a horse on Shabbat, violating a rabbinic law, and was nonetheless stoned, as it had been a Torah violation, to strengthen the seriousness of Shabbat violation. Plus, a married couple who were intimate in a public setting, and the man is flogged, again, beyond the requirement.