Things that are found, and you don't know the halakhic status of those things. For example, coins found out of place in the Treasury of the Temple... Sometimes, the lenient approach is taken, sometimes the stringent - and the mishnah provides the general rule of which is employed when. Also, coins that are found before animal dealers in Jerusalem - always presumed to be Ma'aser Sheni. Why would that be? If found on the Temple Mount - presumed to be "chullin" (not consecrated or designated in any way). Plus a whole host of other factors that might come into play in determining the status of the found items (including if it's meat!). The timing of the finding can have impact as well. Also, whether the context is a predominantly Jewish setting. The more you know about the circumstances, the more lenient the status can be assigned. Plus, a story about a person from Tzipori who bought meat via a non-Jew, which turned out to be non-kosher meat (because the butcher sold non-kosher meat to a non-Jew, making assumptions that the non-Jew would not need kosher meat).