The Gemara doing what the Gemara does - fleshing out details of the mishnah. For example, the mishnah says "produce that's attached to the ground," and the gemara explains: even if it was already ready to be harvested. Ditto for the watch station. Also, when one sells a field when there are trees (of various kinds) in the field - the buyer acquires the trees regardless, but the details should be specified.