Two Lovers star Gwyneth Paltrow has revealed she has a theory about co-star Joaquin Phoenix's odd behaviour. Nominated twice for an Academy Award, Phoenix announced last year that he would be retiring from acting and would concentrate instead on becoming a rapper. He has apparently built a studio in his home and has not signed up for any new movies. But Paltrow seems to believe he has something up his sleeve. "I'm not totally convinced this is his last film. I think there may be something going on. I'm not sure what. I don't know," she said. "I feel like I don't know what he is doing but maybe it's a big performance art film." In Two Lovers, Paltrow plays the volatile neighbour of a troubled young man played by Joaquin Phoenix, who moves into his parents' Brooklyn apartment following a suicide attempt.