Charles, speaking of the forbidden use of curare, says: "What enrages me is that in trained hands such as ours, the drug poses no problem." This is ironic because in the episode "The Light That Failed", Charles nearly kills a patient with curare (albeit accidentally, but still carelessly).
The title is a combination of puns. One is based on the act of refusing to testify under oath in a court of law or any other tribunal (such as a Congressional committee) on the grounds that the answers that would be given could be used as evidence against the witness to convict him or her of a criminal offense under the Fifth Amendment of the United States' Constitution. The other is a reference to the old way of measuring alcohol using the English Imperial amounts. Before going to the metric system, large bottles (like a fifth of Scotch) held one-fifth of a gallon.
Second Battalion of Princess Patricia's Light Infantry was stationed in Korea from December 18, 1950 to November 4, 1951. This dates the episode in spring or summer of 1951. This actually would have been before Col. Potter took command on 19 Sep 1952.
Eight days before Charles Hallahan appeared as "Colin Turnbull" in this episode of "M*A*S*H," he appeared as a cop on "Trapper John, M.D." (a show that, of course, costarred Gregory Harrison, who played "Lt. Tony Baker" in the "M*A*S*H" episode, "The Nurses."