Hullin 95: Keeping Kosher

The case of meat that is held by a non-Jew: what if it wasn't supervised continually? According to Rav - that's prohibited as a caution against the possibility that the kosher meat was swapped out for non-kosher meat. Which leads to a discussion of that likelihood, as the Gemara argues against Rav. Also, if the meat were unsupervised at any time, was it a stringency to not eat it, or was that required? With a story about a ferry and a festival. Which leads into discussion of how the sages used portents -- not quite divination, but some inference from "signs" that are established three times.