Someone recently paid $35,000 at auction for an emerald-green silk gown. It’s backless and a diminutive size 2, so we know that the stiletto-high price wasn’t pegged to the amount of fabric that went into its making.

This striking piece, worn by Keira Knightley in the film " Atonement,” is already regarded in some quarters as on its way to becoming one of the iconic dresses in film history. Someday it could be right up there with the little black dress worn by Audrey Hepburn in “Breakfast at Tiffany’s” and Marilyn Monroe’s fabled white number blown heavenward in “The Seven Year Itch.”

So, what’s going on here? What is it about these garments that squeezes a giggle out of every woman who stands on a subway grate in a skirt or, wearing a simple black shift, admires her reflection in a Tiffany shop window, or yes, shells out $35K for -- admit it -- a frock? Does a dress, whether worn by Audrey or Marilyn or Keira -- posed languorously like a mere wisp in moonlight -- really have that kind of mesmeric power?

Yes, it can. One can imagine the new owner of that emerald-green acquisition taking delivery from the auction house where the winning bid was cast.

The backless size 2 arrives carefully couriered and packaged in bubble wrap. Does the new owner tear open the box and throw on her new purchase, imagining herself a star? Or does she carefully separate each delicate piece of tissue -- wearing white felt gloves -- scrutinize it for a minute, then have it sealed away so it might forever remain exactly as was on Keira Knightley’s oh-so-cinematic body?

Ironically, the costume designer, Jacqueline Durran, still possesses several copies, making the dress decidedly not one-of-a-kind. But to have one of even a few still means having one, and that suffices doesn’t it? I mean, surely that’s worth $35,000, no?

Some could wonder how this apparently extravagant expenditure is much different than the magisterial sum paid for the Diet Coke can Sienna Miller casually threw away that was salvaged, unbeknownst to her, by some cagey, detritus-obsessed entrepreneur.

Said can went up for bid for 10,000 pounds -- roughly $16,700 in American dollars. And it sold.

Or Britney Spears’ used chewing gum placed on EBay for $460. Yes, it sold too.

The difference -- besides the fact that Knightley’s dress appeared in a classy charity auction sponsored by Clothes Off Our Back -- may be that it is part of film history, not some piece of random garbage. And many of “Atonement’s” female viewers swooned as much for the dress as for leading man James McAvoy. But the gown wouldn’t be worth a sliver of its hammer price had it not been moistened by milady’s sweat or tears; sort of like saliva on a soda can or a stick of chewing gum.

We all understand, of course, the obsession with celebrity culture. In the ‘80s, kids would faint when Michael Jackson touched their heads with the electrically charged jolt of some evangelical healer. But as time progresses and the career arcs of these icons begin their inevitable descent, as they become hosts of reality shows and just, well, more human, will a dress worn once-upon-a-time really be worth $35,000?

At the end of the day, Keira Knightley is simply a 24-year-old girl from London with a nice face and a lovely disposition who likes fish and chips and can play a character flawlessly. You certainly wouldn’t pay much for a gown, no matter how beautiful, from your neighbor across the street. Keira Knightley, Sienna Miller, Britney Spears, Marilyn Monroe and, yes, even the lustrous Audrey Hepburn are all “neighbors across the street.” They just drive nicer cars and they can afford that Sub-Zero refrigerator you always wanted.

And they do get to wear wonderful clothes.

image@latimes.com