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Accidentally walking into the bathroom for the opposite sex can be a little disorienting and embarrassing. But actress Felicity Huffman experienced the same emotions when she entered the correct bathroom.

The “Desperate Housewives” star’s confusion occurred while shooting the indie film “Transamerica,” in which she plays a transgender woman born in a man’s body. “Towards the end of filming, I walked into the ladies room and went, ‘Wow, I’m not supposed to be here,’ and I walked out,” Huffman says.

“Transamerica” centers on a transgender woman (Huffman) on the brink of having a sex-change operation to leave behind the identity of Stanley and officially become Sabrina “Bree” Osbourne. Just before taking that final step, Bree learns that she fathered a son named Toby, who is now a 17-year-old street hustler.

In researching the role, Huffman learned of the emotional, social and physical difficulties faced by men who have decided to go through sexual reassignment surgery.

“Either you feel alienated from yourself, or you actually do it and you’re alienated from society–you’re an oddball,” she says.

The challenge for Huffman was to play a biological male who is learning how to express femininity–with varying success–through makeup and clothes.

“[Bree] doesn’t want to go makeup shopping and go to the counter and ask ‘What base do you think I am?’ So she does it through the mail. It’s got to be thick because it’s got to cover any stubble. She’s had 350 hours of electrolysis, but there’s still stubble,” Huffman explains. “The costumes were all catalog and cheap because Bree wouldn’t go clothes shopping. She didn’t know what color looked best on her. Lavender is the color of transformation, so she’s going for that.”

Probably the toughest physical challenge, however, was finding her transgender voice since she didn’t have the chest capacity to create the necessary resonance to sound male.

Because of the difficulty of creating the voice, Huffman found it easier to stay in character the whole day during filming.