Revealing mistake: After many hours in the OR Hawkeye takes a seat in the wheelchair that Radar's pushing, and when they reach the Swamp there's a wooden ramp on the ground right outside the door, which is never normally there, deliberately placed for this shot so Radar can push the wheelchair into the Swamp.
Continuity mistake: While Radar and Hawkeye are in the mess tent, after Hawkeye cracks a joke about how the cook sculpts grease into the shape of lamp chops, between shots facing Radar and the shots facing Hawkeye we see Radar either holding bread in his right hand or a fork.
Continuity mistake: When Trapper and Hawkeye are sitting outside the Swamp, Hawkeye pours the martinis from the tall glass beaker, and in the shots facing Hawkeye there are quite a few large ice cubes in the beaker, but in the shots facing Trapper there aren't as many ice cubes floating in the beaker.
Visible crew/equipment: At the end, after Father Mulcahy says goodbye to Sarah, when it cuts to a wideshot we can see two actors' rubber T-marks on the ground. The first is behind Father Mulcahy's feet, a white T-mark (albeit dirty) where Sarah had been standing, and the second becomes visible when Klinger runs over and bumps into Kellye, he kicks up some dirt which causes the black rubber T-mark to flip up off the ground.
Visible crew/equipment: After Radar walks into the Swamp and gives Hawkeye and Trapper the coffee and case folders, just as Radar tells them that he was too sleepy he walks out, and the actor's chalk T-mark can be seen on the ground (although faint, it's distinguishable).
Visible crew/equipment: When Klinger wakes up in post-op, Margaret, Hawkeye, and BJ are happy he's awake, and in Klinger's first close-up when he asks about Weston the shadow of the boom mic can be seen at the top left corner of the screen, and in his second close-up a bit of that shadow is still noticeable as it moves out of shot.
Continuity mistake: When Klinger's stopped by the MPs it cuts to a close-up of the Polaroid camera and it's lying between the seats with its hand strap facing the front of the jeep, but when Klinger picks it up the camera's positioned the opposite way with its hand strap facing the back of the jeep.
Continuity mistake: While Colonel Potter is painting the portrait of Charles, the portable military field desks behind Potter are all open - note the front doors are flipped down, but in the closeup of Charles holding the painting of himself the doors are folded up. And the books, etc. atop the field desks change as well.
Continuity mistake: While Charles is reading the letter about his nephew being discharged because of fainting spells, Klinger feigns a fainting spell falling forward onto Hawkeye's cot, and his body lies lopsided with his leg hanging off, but when it cuts to the next shot Klinger's perfectly positioned on the cot. Also, note the mail Klinger tossed earlier onto Hawkeye's cot, near his pillow, is now neatly tucked under the blanket towards the foot of the cot.
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.