Visible crew/equipment: A crew member is visible in Margaret's tent when she confronts OR nurse Helen about her drinking, approximately halfway through the episode.
Revealing mistake: In the supply room, as Hawkeye lights two candles, the room gets noticeably brighter. However, there's too much light for two candles, and his shadow comes from above.
Visible crew/equipment: In the last scenes of the episode, the overhead shots showing the parade where Klinger rides in on Sophie, dressed (undressed) as Lady Godiva, you can see the boom mic in view at the top of the screen.
Continuity mistake: As Mulcahy enters and is introduced by Potter, he assumes the podium, and clasps his hands behind his back. A second later, his arms are by his sides.
Revealing mistake: In the closing scene, as the camera looks at the collected crowd, the camo net over the building poorly hides the edge of the "sky" background and the sound stage walls.
Continuity mistake: While Charles, BJ, and Hawkeye are in the Officers' Club, when Margaret storms in and starts yelling at Charles about the visiting pervert Colonel, Charles facepalms himself with his right hand, but next shot his left hand is up, and it continues to switch.
Visible crew/equipment: At the start, when BJ calls Hawkeye "twinkle toes" before Hawkeye leaves, the edge of the Swamp set can be seen at the top, left corner of the screen.
Father's Day - S9-E4
Continuity mistake: As Margaret sits on the bunk to talk with Al, his hands are by the table's edge. When the angle changes, they're up at chin level.
Tell It to the Marines - S9-E8
Continuity mistake: The water Klinger accidentally spits on Potter goes from a number of separate spots to one big spot in a couple of seconds.
Other mistake: Charles starts a discussion on the army having forbidden the use of curare. The following chatter is all about how things in the M.A.S.H. OR have slowed after curare was banned, leaving us with no choice but to understand that the ban came into effect during the Korean War. Actually, curare was not approved for use by the U.S. Army at any time during the Korean War. (See "Notable Names in Anasthesia" - J. Roger Maltby, Royal Society of Medicine, Great Britain, pg. 14). (00:00:25)
Suggested correction: The whole point of the discussion is to make it clear that curare was never allowed for use by the US military, however since the majority of the doctors there are not enlisted, they know of curare and how to use it on a patient. At no point is it mentioned that the banned occurred during the Korean war.
While they never specifically say that the ban occurred during the Korean war, at the beginning of the episode, Charles says "Ever since the army forbade our use of curare..." Then at the end of the episode, COL Potter says "It sure is the cat's P.J.s having our curare back." after they get some supply from another non-American unit. These conversations imply that the doctors had been allowed to use curare by the army until this point and the ban by the army is why they aren't using it any more.
Father Mulchahy says "I've noticed the work goes much faster with curare." Father Mulchahy's only experiences in operating rooms are from his deployment at mash 4077 (he mentions he used to work with children before the war), so he must have "noticed" it there. This makes it clear as daylight that curare was used at mash before it was banned.
Cementing Relationships - S9-E3
Other mistake: When the mistake in the cement is discovered, Klinger is addressing Pierce, saying "Mr. Putty Putty, here." Problem is, that it was Mulcahy singing, "Cement mixer, putty putty.
Factual error: When BJ opens the first box of tongue depressors the tongue depressors are packaged in a plastic bag inside the cardboard box, my research says that plastic bags were not available in the early 1950's. (00:08:06)
Continuity mistake: In the Officer's Club, Potter is about to order a drink. When he goes to give the order, he starts to look at Hawkeye. When the camera cuts to a close up of Potter, Hawkeye, and BJ, he's facing forward again.
Tell It to the Marines - S9-E8
Continuity mistake: In the mess tent, after Hawkeye and BJ read about the blood donations, Hawkeye goes to fold and put the paper down. When the camera cuts to a wide shot, he's folding and putting the paper down again.