Most people can't keep a secret. But when a movie with a twist ending comes out, the surprise often stays hush-hush — even after the film's release. 

It's happened with "The Crying Game," "The Usual Suspects," "The Others" and "The Sixth Sense." And with Friday's release of "Matchstick Men" — a part con, part relationship flick with a twist that caught even director Ridley Scott (search) off-guard when he read the script — the code of silence will be tested again.

"I think we'll be OK as long as you guys don't give it away," said "Matchstick" co-writer Nicholas Griffin (search) at a recent press roundtable in New York.

But what keeps people's lips sealed about a film's surprise?

"As a critic, the last thing you want to do is give away the twist or the ending of the movie," said E! Online movie columnist Anderson Jones. "It dilutes the movie-going experience, which can occasionally be filled with surprises."

Jones said the Miramax picture "The Crying Game," (search) which contained a major shock mid-movie, was the first time a studio explicitly asked reviewers to keep a plot-turn under wraps.

"They gave letters to critics and implored them not to tell anybody," Jones said. "Since then, I've seen a lot of letters saying, 'There are surprise endings in the movie. Please keep it to yourself so that everyone can enjoy the movie in the same way.'"

Certain films like "The Crying Game" and "Adaptation" hinge on character changes that leave audiences with a kind of whiplash in the middle of the movie. Others like "The Usual Suspects" and "The Sixth Sense" unveil a revelation in the final moments that changes the entire meaning of the film. But in all those cases, the secret managed to stay that way. 

Some of those involved with "Matchstick" discussed the grand finale but made it clear they didn't want the press to let the cat out of the bag.

Lead actress Alison Lohman (search) — who plays Angela, the daughter of con artist Roy (Nicolas Cage) — skirted the issue when asked twist-related questions.

"I wouldn't want to talk about that because that's not what the story is about for me," Lohman responded to one journalist. "I don't know how you guys are going to handle that. I wouldn't want anybody to know."

When asked whether the cast and crew held meetings about how to talk — or not talk — about the "Matchstick" surprise, Sam Rockwell (search) (who plays Roy's partner-in-con Frank) said they did.

"You guys aren't going to give that away, are you?" he asked. "That's important because we don't want to give away the ending."

But keeping the secret has become a tricky task with the advent of Internet movie gossip sites, some of which seem to find sadistic joy in spoiling films for those who haven't seen them.

"Tons of fan sites think it's clever and fun to blow the endings of movies," Jones said. "It's a dumb, dumb thing to do."

Filmmakers are fighting back, but only by doing the same thing as the gossipmongers.

"Now what you're seeing is producers and directors going on the counterattack and giving away their own spoilers," said Jones.

For his part, Jones doesn't write about crucial plot points — unless he deems it newsworthy or thinks it will entice people to see the film.

"I would be willing to reveal a spoiler that makes the movie worth seeing, but not one that ruins the whole movie," he said, adding that he includes a warning in his column if he's going to reveal a plot-turn.

There isn't a written code of ethics reviewers adhere to in their tight-lipped handling of twists. But when critics and audiences band together to keep the secret, new viewers can have the same reaction "Matchstick" director Scott did when he first read the script.

"When I hit the twist, I couldn't believe it," Scott said. "I am a really cynical reader and I had not seen it coming."