By Patrick Gerard Healy

Globe Correspondent

     When the film ''The Departed" comes out next year, there's one scene with a young, brown-haired guy wearing a slightly worn denim jacket standing in a subway car. It might be hard to notice him in the tightly packed crowd, particularly with the camera focusing on Martin Sheen and Leonardo DiCaprio chatting covertly on their cellphones.
     That is, it would be hard to make him out if you aren't my mom.
     I recently took part in the scene with 149 other local extras in Martin Scorsese's latest film. The only requirements: Dress for early fall (meaning no bright clothing and not too much skin showing), look as average as possible (meaning not like a star), and be available to work two consecutive nights, from 11 p.m. to 5 a.m. (meaning desperate enough for a minuscule part in a movie to forgo sleep and wear the same clothes two nights in a row).
     The call for extras at South Station brought senior citizens, a full rainbow of ethnicities, lunatics, and scores of college kids.
     When we arrived at the station's upstairs food court, a crewmember assigned everyone a number, hastily described what he knew about the scene, and detailed the don'ts: no photographs, autographs, or chatting up the stars.
     The only do: Do what you're told.
     For each night, they paid $94.50, a figure that made me better comprehend how movie budgets can rise to multimillions of dollars. For just a few minutes of the film -- and it may be less, or not even make the final cut -- the scene cost nearly $30,000. Just for the extras.
     On the Red Line platform, we learned one subway car would have the stars in it, while the other would be full of extras, most of whom would be recognizable only as blurry thumbprints behind the glass of the adjacent car.
     A production assistant instructed a third group to wait on the platform.
     Of course, every extra wanted to be in the car with the stars, a desire that created a mix of resentment and envy.
     I got lucky. I walked toward a woman pointing ''you, you, and you," fell in line in front of her finger, and suddenly found myself in the right car.
     Inside, the crew mapped out the positions where we would stand for the next five hours, riding back and forth from Park Street to South Station to Broadway, shooting multiple takes of the same short scene. A diagram of the car, with our numbers noted, ensured we kept our places.
     Small changes came constantly. Evan Dahme, 22, a Northeastern student, was told to act as Emerson senior Susan Chaves's boyfriend. But on the crew's second walk-through, they nixed Dahme. His blond hair was ''too bright," they said. Chaves, who has distractingly stunning eyes, didn't last much longer.
     ''It was kind of disappointing, because I was right next to Leo," she said.
     The girl who did end up next to Leo was Laurie Ortiz, 21, a Northeastern student. ''It was kind of surreal," she giggled. ''I still have his posters on my wall from 'Titanic.' "
     Despite the competition for visibility, the extras bonded between takes. DiCaprio kept to himself, but Sheen let down his guard, regaling those in earshot with song trivia and tales of his 1961 wedding.
     Standing next to me was Paul Motyka, 65, a retired engineer from Acton. One of several experienced extras, he told of how he ended up on the cutting room floor of ''Mystic River."
     ''I look for different things to do to broaden my life experiences," he said, knowing his time may again be for naught.
     On the second night, an extra on the platform slipped into the train and edged toward DiCaprio.
     ''So do you like being called Leo or Leonardo?" the man asked.
     The star muttered that it didn't matter.
     ''What do you think of our sports teams?" the man persisted.
     DiCaprio just shrugged.
     We broke a few hours later, around the same time morning did.
     I walked into the awakening city more aware of the absurdities of show business.
     It was fascinating and repellant at the same time. Through the smallest hours of morning, we stood around in a small subway car.
     Still, for some reason -- for the proximity to stars, the possibility of being up on the big screen, whatever it was -- we were just happy to be a part of it.