James Sweeney on Olsen Twins, Toe-Sucking and Dylan O’Brien

SPOILER ALERT: This story contains spoilers from “Twinless,” now in theaters.

James Sweeney has a thing for twins. In his new quirky dark comedy, “Twinless,” he and Dylan O’Brien play Dennis and Roman, two men who form an unlikely friendship when they meet at a support group for people whose identical twins have died.

In one scene, Dennis is shown watching Mary-Kate and Ashley Olsen in their 1995 comedy “It Takes Two.” Sweeney, who wrote and directed “Twinless,” reached out to the former child actors with a letter. “I think I espoused my love for them and begged them to use their likeness from the classic ‘It Takes Two,’” he recalls. “Incidentally, they’re not playing actual twins in the movie. They’re just playing people who look identical to each other.”

Since the film’s premiere at Sundance earlier this year, many have been assuming Sweeney has a twin in real life – he doesn’t. “I think twins were very much embedded into the cultural zeitgeist of my childhood,” he explains. “It wasn’t just the Olsens, but also ‘Sister, Sister’ and ‘The Parent Trap.’ And for me, being a military brat and having to hop around and start over a few times, I think it was sort of that fantasy of the perfect best friend who shares your sentences and wants to do all the activities you want to do. It was very appealing to me.”

O’Brien not only plays Roman but also portrays his twin, Rocky, in flashbacks. “I wanted somebody who I believed would have the versatility to pull from different characters, not just in terms of physical and emotional transformation, but also tonally, comedic and dramatic. I think that’s something that Dylan has in spades,” Sweeney says. “And even though I felt confident in that, getting to know him and then developing the film and working with him, it really surpassed my wildest dreams. I think he’s truly a chameleon, which I find to be rare in somebody who is…