The pretty ROMEO + JULIET star's character, MIRABELLE, disrobes for her first love scene with 60-year-old Martin in the story, which was penned by the actor himself.
And Danes admits it was far from easy to bare all.
She recalls, "A friend told me, 'It's good you're doing it at 25. When you're 80, you'll look back on this and think, I was pretty firm, so there's that.'
"It was uncomfortable, I have to say, but I did think that it was relevant and useful. Also, it's erotic. There's no reason to pussyfoot around that. I thought it was vital, so I stripped."
Danes insists she had no more problems stripping in front of Martin than she would have before someone of her own age.
She adds, "You're not supposed to be kissing somebody who's not your boyfriend. You're just not. I don't know when I'll become more comfortable with it. You have to depersonalise it."
Danes also found the sex scene wasn't the only difficult thing to shoot - she also struggled with a kissing scene with pal Jason Schwartzman.
She recalls, "We both did shots of vodka before we had to kiss... It was just too creepy."