Sienna Miller and James Franco have contracted the costar disease, in which normally platonic coworkers on a film set begin getting too close for comfort. TMZ reports that the two, who now wear matching clothes, filmed a kissing scene that lead to a quick pairing offscreen: "During filming Friday afternoon, the leading pair had to roll around in the hay kissing as Franco's shirt was off. Once the set wrapped, sources say the couple took their on-set frolicking off-set, well into the evening."
"The two took in a concert and were seen canoodling and dancing in the streets together. Around midnight, Miller and Franco got some Chinese food, enjoyed a cigarette together, and hit the nightclubs."
Dating Alfie costar Jude Law worked so well, Sienna has moved on to a new costar. I give this two months, tops.