Father Mulcahy says he hadn't saved anyone's life before until his friends remind him that he already saved the life of an alcoholic dog. However, the earlier fifth season episode, "Mulcahy's War," had Mulcahy saving a wounded soldier's life by performing an emergency tracheotomy under enemy fire following Hawkeye's radioed instructions.
One of the letters Charles opens contains a leaf which is identified as a birch leaf. It is in fact a maple leaf.
Dogs do not tolerate alcohol well. Letting the dog, Irving, drink "as much as he wants" would likely kill the dog.
Throughout the episode, Loretta Swit's fingernails can be seen at over an inch long. No nurse, especially a head nurse, would have fingernails that long.
When Maj. Houlihan is talking with the patient, her rank insignia is worn upside down. The "stem" of the oak leaf should point to the edge of the collar not towards the wearer.
When Charles is speaking and writing out an answer to the letter of the kid who is jealous, he is obviously not writing words, as two of the words he says are longer than what his pen is doing on the paper.
When Margaret is shown reading the letter in her tent (as well as Hawkeye's and Father Mulcahy's when Hawkeye is seeking guidance from him) none of the pages the letters are written on appear to have lines, although from the holes punched on the side of the papers suggests it is from the students (4th grade) notebooks and as such it is also missing is ragged edges from where a page would have been torn out of said notebooks.
As Charles replies to the girl who sent the leaf, his Boston accent slips in the voiceover, as the last word, "heart" is spoken with the actor's normal midwestern accent.
Hawkeye's schoolteacher friend back home sends him a package of letters, written by her pupils, because Hawkeye had said how bored 'everyone' is. But he only passes out the letters to the main group, BJ, Col. Potter, Margaret, etc. He doesn't give any to the rest of the bored people in the camp.
When Rosie is throwing Irving out of the bar, she is yelling in English. Since she is by herself and doesn't know that Father Mulcahy is outside, she should be speaking in her native Korean.