Lorene's speech at the end - is she lying or is she only repeating a lie that Warden told her? She mentions speaking to Prew's mother (and he implies his parents are dead earlier in the film), suggesting it's the former. There's also the possibility that Warden lied to her but she knew it was a lie and is still choosing to go along with it.
How in love with Warden is Karen really? She outright says she's had multiple affairs before. Maybe she's had many steamy beach rendezvous with other men (as Warden suspects initially) - and still just wants the perks of being the wife of an officer. Or she could genuinely love him but be so depressed that she assumes he doesn't love her the same way. It's also left open as to whether or not she's going back to the States with or without her husband at the end. She seems somewhat hopeful that she might return to the island one day, hinting that she may go back to try again with Warden one day.
Did Lorene/Alma come to love Prew for real? Is it just a fling as she suggests early on - to keep herself from getting lonely? Or was she genuine when she offered to marry him?
Award Snub: Many people feel that Deborah Kerr should have won for her wildly against type performance as Karen. Ditto for Montgomery Clift, who even the director regarded as the real workhorse of the film.
Common Knowledge: The rumor that Frank Sinatra only got his role due to his Mafia connections, cemented in popular culture by The Godfather, has never been substantiated. Everyone involved in the movie denied it, including Eli Wallach, the original choice to play Maggio; Wallach had been cast in Tennessee Williams' play Camino Real and preferred that role to the film, leaving the door for Sinatra to take the part.note For his part, Sinatra was extremely grateful to Wallach, though he would always needle him by saying, "Hello, you crazy actor!" whenever they'd meet publicly. Understandably this issue became a lifelong Berserk Button for Sinatra, who frequently threatened to sue newspapers and magazines repeating the story, and once publicly confronted Mario Puzo after The Godfather's publication. The reason he was cast is that Ava Gardner was shooting a film for Columbia and suggested him. Studio head Harry Cohn signed him on because his stock was low and that meant he wasn't likely to charge much.
Ensemble Darkhorse: Both Maggio and Karen are the most remembered characters in the film. The former for the fact that Frank Sinatra really showed his range, and the latter for the shocking Fanservice she provided.
Foe Yay: Judson's treatment of Maggio has the subtext of sexual abuse. A modern viewer is likely to assume Prison Rape was involved at some point during Maggio's time the stockade.
This was Frank Sinatraís first foray into serious acting after plenty of musicals.
After numerous films of, as she put it "poke her up the ass parts", Deborah Kerr showed Hollywood her range. English audiences had known she was more versatile anyway.
Ho Yay: There's rather a lot of it between Prewitt and Maggio, especially in the latter's death scene. Given that there was plenty of homosexuality in the book (and it had to be censored for the Hays Code), this is probably intentional.
Jerkass Woobie: Karen may be cheating on her husband but she's depressed and trapped in an unhappy life. The fact that she had to suffer a miscarriage because her husband was too drunk to call a doctor for her pretty much sums it up.
Memetic Mutation: Every movie or TV show that has featured an oceanside love scene has been assumed to be paying Homage to this film.
Narm: The Insistent Terminology that Lorene is a 'nightclub hostess' and not a prostitute can be hilarious to watch. The club is clearly a censored brothel, and it's obvious the filmmakers had no intention of hiding it.
An urban legend has since arisen that Sinatra got his Oscar-winning part thanks to his mob connections. That hasnít been proven, but it did inspire the Johnny Fontane storyline in The Godfather.
A similar urban legend is that George Reeves had his part cut down after test audiences kept going "there's Superman" - which has been denied by everyone who worked on the film, and no extra scenes for him are in the shooting script. Didn't stop the movie Hollywoodland from saying it was true.
Ernest Borgnine, while filming Marty, went into the Bronx to get into character for the role. While there, just walking around, he was harassed badly by some local toughs who were enraged that Borgnine's character in From Here to Eternity, Sgt. Judson, had killed Frank Sinatra's character. He was only able to calm them down by explaining that in reality, he was good friends with Sinatra, as well as being a fellow Italian-American.
One-Scene Wonder: The Deadpan Snarker girl who welcomes Prewitt on his first night in the club. She sees him eyeing Lorene and then snarkily says she's going to talk to someone else "because I can see I'll be of no further use to you."
Maggio's death in Prewitt's arms, and Prewitt's tearful rendition of Taps on bugle afterwards.
Anticlimactic as it seemed, Prewitt's death, and Alma's tearful but composed scene with Karen afterwards as the latter throws her leas into the ocean, telling Alma that if they float towards shore, it means that they'll return to Hawaii later. Alma tells her that she's never going to come back.
The brothel of the book is censored to a Gentleman's Club and the whores become 'hostesses' because the Hays Code wouldn't allow for such a thing.
Likewise Karen's infertility in the book is caused by her husband infecting her with gonorrhea he caught from one of his affairs - but changed to a miscarriage in the film because the code forbid mention of any STD.
Part of the conflict in Karen and Warden's affair is that Karen won't get a divorce unless Warden becomes an officer. Divorce was possible at the time but a woman was still looked down on for it - so Karen wants to remain somewhat respectable (leaving her husband for an officer). Additionally it's clear that her husband is supporting her, so she's after financial security too.
What An Idiot: After his big attempt at a heroic return, Prewitt gets shot and killed... after refusing to halt while sneaking around suspiciously to rejoin his company after Pearl Harbor. It's not even that he needed to avoid punishment, as he already told Alma he needed all the help he could get.