The rabbis instituted takanat hashuk to protect buyers from responsibility from buying stolen items. The takana is that if someone claims that the item is theirs, they can take it back but need to reimburse them the amount that they paid for the item. Does this apply also in the case where the thief was caught? Can we always believe the original owner when he claims it was stolen? What other evidence does their need to be to allow him to take the item he claims is his? If two people are walking and one is losing his expensive item and the other dumps his item to help the other save his more expensive item – if he does it without being asked, he can only demand back money for his time but not for the item he dumped. The gemara questions why we don’t assume that the first item (the expensive one) was already hefker (ownerless) as the owner knew if would be gone in a minute and gave up ownership of it), in which case the other one could take it as his own. VArious braitot are brought which seemingly contradict each other regarding items that are about to be lost – and the gemara reconciles them.