Spreading a mat over a beehive to protect it from the weather - the mishnah says it's acceptable; the gemara raises questions as to when and to what extent that is the case. The Gemara also makes it clear that the focus is the needs of people - to protect the honey, for example, whereas when there's little or no honey to be found, the question of the permissibility of protecting the beehive becomes sharper. Also, the muktzah that is set aside because it's disgusting. Abaye asks what to do, and then reasons it out for himself, to his eventual chagrin - specifically, the placement and inevitability of excrement. Plus, a new mishnah outlining the various ways we might think that Shabbat and yom tov are different, but are not - specifically, rabbinic enactments, optional practices (on that date), and even fulfilling mitzvot.