"I lived as a stripper for a year," she says, a hint of a smile on her doll-like face.
But, that's not all.
The actress, whose beauty has attracted some of Hollywood's most eligible bachelors over the years, including Heath Ledger, Ed Burns and James Woods, has a bigger bombshell to drop.
"Actually, I lived as a stripper-prostitute," the 39-year-old continues, a revelation somehow missed by every tabloid magazine and gossip website in the world.
"I got into prostitution and it was really informative."
Las Vegas makes visitors say and do strange things.
It could be the dry desert air.
It could be the two litre glasses of icy beer or margaritas offered for sale on every street corner or in every nook and cranny in the cavernous casinos.
This interview takes place in the afternoon and we are perched high in a suite in Caesar's Palace, one of the Vegas strip's largest casinos. Caesar's Palace is the setting for Graham's new blockbuster comedy, The Hangover, which opened number one in North America on the weekend with a phenomenal $US44.979 million ($NZ70.9 million) in box office tickets sold between Friday and Sunday.
Early buzz was so strong for the movie, directed by Old School's Todd Phillips and also starring Bradley Cooper and Ed Helms, a sequel was set in motion months ago.
The film appears to follow a common story-line - bunch of dudes go to Vegas for a bachelor party, drink too much and get into big trouble.
Phillips and the film's screenwriters, Jon Lucas and Scott Moore, pull out a few tricks, twists and turns along the way, leading film critics like The Los Angeles Times' Betsy Sharkey to write: "There is a sort of perverse brilliance or brilliant perverseness to be found in this story of a bachelor party gone terribly wrong".
But, back to Graham.
The actress, who was nominated for an Independent Spirit Award in 1990 for Drugstore Cowboy and was praised for her 1997 performance as a porn star in Boogie Nights, has had some tough career knocks in recent years. The low point was in 2006 when she made the move to TV to star in a sitcom, Emily's Reasons Why Not.
The series had such a poor debut US network ABC yanked it off the air immediately, refusing to show more than one episode.
Graham appeared to disappear.
In The Hangover Graham plays Jade, a stripper-prostitute, who happens to hook up with the bachelor party fellas during their wild night in Vegas.
As a devoted actor, Graham says she delved into stripping and prostitution to fully prepare for the role. It is what Robert De Niro or Al Pacino would do, right? "I'm really method, so I thought I had to get into it," Graham said.
Just when her story seems convincing, she comes clean.
She is messing with her interviewer.
"I didn't really get into prostitution," she laughs, destroying what would have been a world exclusive.
Graham did do some preparation for The Hangover.
"Tonnes of training," she says.
"Just drinking a lot, getting hungover and drinking more and things like that.
"My friend teaches pole dancing.
"I had taken some of the classes before I got the job, but I went back and took some refresher courses." Graham and Phillips also visited strip clubs, although she was disappointed with what she saw.
"It is kind of sad," she sighs.
"I miss the dancing strippers.
"Now they are just gyrating strippers doing the lap dance. There is not really a stripper who does a dance.
"What happened to that? "Why did they stop doing that? "What's the deal with that? "As a girl, I like to see a girl do a dance."
With her career back on track following the huge box office debut of The Hangover and with several other films set for release, including the British comedy about the London art world, Boogie Woogie, and the drama-comedy, Son of Mourning, Graham is enjoying life on and away from the set.
She is also branching out, attempting to produce a number of projects and has written a script for a movie about witches.
Her love life has also blossomed.
Soon after completing Son of Mourning in Florida she began a relationship with the film's director, 32-year-old Yaniv Raz.
While Graham lights up talking about Raz, her face dims when the conversation switches to Ledger. Graham and Ledger dated for almost a year, breaking up in June, 2001, after reports surfaced of the Australian actor making out with a model in Manhattan nightclub, Lotus.
"I like Perth," she says, recalling a trip she took with Ledger to his hometown.
"The beach there was really fun. I stayed at a hotel right on the beach and I don't know why, but there was this little falafel stand right underneath.
"I just have this vivid memory of eating falafels on the beach and walking down the beach with the sun setting."
Ledger died from an accidental prescription drug overdose in January 22, 2008. Just over a year later he was named winner of the best supporting actor Oscar for playing The Joker in The Dark Knight.
"I'm very happy for him that he won," Graham says.
"That's great." Graham also had some kind words about Ledger's father Kim, mother Sally and sister Kate, who accepted Ledger's Oscar.
"They are so sweet. They are really cool." The Hangover opens in Australian June 11.
