A striking feature of Talmud study is how it seamlessly moves from subject to subject; and how, almost out of the blue, one finds oneself discussing something that seems totally disconnected from the original discussion. The Mishnah discusses the case of a person who mistakenly makes the brachah of boreh pri ha-etz on a vegetable, ruling that one must repeat the proper bracha of boreh pri ha-adamah. The Gemarah questions the need for such a ruling, as why should one think that one fulfills his obligation by claiming a vegetable grows on a tree?
As the Talmud is, at its core, an oral tradition—with the words before us a summary of “classroom”” discussion—it is not surprising that debates will occur as to what the “teacher” actually said.
The opening Mishnah of the sixth chapter of Brachot discusses the various blessings one makes on different types of food. The Talmud attempts, but is unable, to find a scriptural source that tells us that one must make a blessing before eating, finally concluding that we need no source. It is a sevarah, a simple, obvious, logical inference that one must bless G-d before we eat, as "it is forbidden to benefit from this world without a blessing". Verses in the Torah are (generally) needed only to tell us that which we would not otherwise know.