Character mistake: In the opening scene, Hawkeye and Trapper are operating on a two-star general. But neither one of them or the nurse is wearing their masks. They are under their chins.
Continuity mistake: When Klinger imposes himself between Oksun Li and Crosetti, he puts his hands on his hips. When Crosetti gets up, Klinger gestures with his hands which then drop down on either side. A split-second later they're on his hips again.
The Late Captain Pierce - S4-E4
Other mistake: When Digger shows Hawkeye the copy of the death certificate, Hawkeye steps out of the shower stall and its door swings back and forth. As Hawkeye wipes his face with the towel, we can see the top of the flesh colored covering Hawkeye is wearing. (00:08:05)
Goodbye, Farewell, and Amen - S11-E16
Continuity mistake: When Hawkeye is returning to camp, he and his driver completely pass some Burma-Shave signs the other have set up to welcome him back. An ambulance bus is a few feet behind them and manages to then suddenly appear at least 30 feet behind them to smash all the signs.
Factual error: Radar's mother's boyfriend owns a Nash Metropolitan, a car that was not produced until after the end of the Korean War.
Continuity mistake: In one episode, Frank's middle initial is M, then later it's D. His full name was Franklin Delano Marion Burns.
Audio problem: As Roy and Loraine enter the camp, you hear a "YEE-HAW" from Roy, but if you watch his mouth, you see he really says "YAHOO."
Preventative Medicine - S7-E22
Continuity mistake: In Potter's quarters Klinger's arm holding the chicken goes from in front of his chest to by his waist between shots.
Factual error: The Spot-A-Card pinball machine in the Officers' Club didn't come out until the 60's.
Revealing mistake: As the first chopper lands on the pad, you can see that the pilot is Cowboy, a clear reuse of the shot from the episode "Cowboy"
The General Flipped at Dawn - S3-E1
Continuity mistake: As the chopper lands on the pad, and the ambulance comes up, the pilot is as two different men when Hawkeye and Trapper approach and arrive at the chopper, meaning the landing was stock footage.
Good-Bye Radar: Part 2 - S8-E5
Other mistake: As the camera cuts to Hawkeye and Margaret working, the man behind her is holding a chest X-ray, but it's upside down, which would be useless as a guide.
Deal Me Out - S2-E13
Continuity mistake: From behind, Klinger's cigar is full length, with no signs of being lit. When he responds to Hawkeye's question, it is noticeably shorter.
Last Laugh - S6-E3
Character mistake: BJ refers to his friend Leo as colonel. He's wearing two silver bars, insignia of a captain.
Factual error: When the can of beans explodes all over Hawkeye and Hotlips, they act as though the beans are cold. In fact the beans would have been at boiling temperature as the can overheated, causing it to explode, and the two would have been burned.
Revealing mistake: When Sherwood has died on the gurney, with Roberts holding his hand, after breathing stops, you can see the bandage on his neck still jumping in time with his pulse.
Factual error: Out by The Gun, Hawkeye's Captain insignia on his garrison cap is missing the lower corner of one bar. So, it would be considered unserviceable, that is, unfit for use, and should have been replaced with a new insignia.
Suggested correction: While that is true by the Army's standards, it is entirely in character for Hawkeye not to give a flying you-know-what about the state of his insignia.
True, but even he knew that correcting it sooner rather than later would be wise. But, as always, I bow to your knowledge.
Revealing mistake: In Margaret's tent, while she is getting ready, if you look at the central pole you can see the cut where it is supposed to break when Frank hits it.