The 39-year-old TV personality, who will make his Broadway debut in "Of Mice and Men", said it is different than films as it gives you time to rehearse, said the Hollywood Reporter.
"There's something really refreshing about that where you feel a deeper connection to the character. I've hear other actors say it too - you realise how deep you can go into a character," Franco said.
"In movies, we hardly rehearse. It's like, you're ready to go when you're there, you only ostensibly have to get right only once, and then you move on. Here, you're etching it, and there's something kind of zen about that," he added.
His character is of the uneducated but quick-witted friend and protector of simple-minded Lennie (O'Dowd), a gentle soul unaware of his own strength, in John Steinbeck's tragic story of two itinerant workers seeking new opportunities in Depression-era California.
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Franco also plugging his new poetry book and "Maladies" film to Jimmy Fallon and mentioned that he's been making a short version of Harmony Korine's "Kids."
"It's Harmony Korine, who directed Spring Breakers -- when he was 18, he wrote Kids, and this is a short that he wrote around that time that he gave to [director] Larry Clark to get the job to write Kids. It was never made, so I'm making it now," Franco said.