When a scholar of halachah, who is discussing the activities forbidden on the Sabbath, wishes to specify those activities connected with the extraction of food from that within which it is held, he calls them "threshing."
He selects one characteristic activity from the totality, a highly concrete and specific item, and makes it the key imagery word for the concept.
So that a person who milks a cow on the Sabbath can be said to have transgressed the law against "threshing."
–Rabbi Adin Steinsaltz
From "The Imagery Concept in Jewish Thought" in The Strife of the Spirit, p. 65, by Rabbi Adin Steinsaltz