The amount of blood and location on the Lt's shoulder wound changes. When he and Charles first go into the OR, there's a lot of blood at the top of the shoulder. By the end of the storyline, the amount of blood is much less and has been lowered to the lapel of the pajamas.
Radar's rabbit is clearly an adult, but the pregnancy test calls for using an immature female rabbit. Specifically, injecting the rabbit with urine from a pregnant woman would cause the ovaries to mature and enlarge due to the hormones in the urine, and the ovaries would be examined. The test is useless if the ovaries have already matured.
When Hawkeye, Potter, and Margaret are drinking in Potter's office, Loretta Swit can be seen with very long fingernails, which would not be allowed as an Army head nurse.
Near the end, when Klinger slaps the ground in frustration, the sound is that of his hand hitting the sound stage floor, not the ground outside.
Lt. Martinson's sidearm is incorrect. Military issued 45 pistols do not have the round bobbed hammers.
Lt. Martinson asks Maj. Winchester to pass him his pack, and when Winchester does, Martinson pulls out his pistol and takes Winchester hostage. However, Season 4's "The Gun" established that it was standard operating procedure for Radar to safeguard all weapons from wounded soldiers and lock them in the camp's gun bin until a wounded soldier was released from the hospital and being returned to his unit. So, Lt. Martinson's pistol should not have been in post-op with him.
After Hawkeye and Margaret tell Col. Potter about Margaret's possible pregnancy, Col. Potter breaks out a bottle of gin (or possibly vodka). Margaret then has several shots. But a head nurse should know better than to drink alcohol if she may be pregnant; as well, neither Hawkeye nor Col. Potter -- both surgeons who should also know better -- dissuade her from indulging. (This actually incorrect. Fetal alcohol syndrome was not discovered until 1973. In the 1950's, pregnant women were encouraged to drink in moderation.)
When Klinger claims that the children in numerous pictures are his, Potter estimates the age of one of them to be nineteen, and says that would have made Klinger a father at eleven, implying that he's thirty. If he were that old, Klinger would have been subject to the draft in World War Two.