That three-day-old report about Angelina Jolie having learned from a private investigator that Brad Pitt and Marion Cotillard were having it off during the filming of Allied has been denied by Cotillard. On top of which it’s none of our damn business. But I can at least mention how things work when an affair ignites between the stars of a film. (Such things happen with more regularity than you might think, and between big names.) The general rule is a variation of “what happens in Las Vegas, stays in Las Vegas.” Nobody says anything when a power couple is up to something, and when the movie wraps so does everything else. Those are the rules that almost everyone understands and lives by. Every now and then an on-set relationship will spill over into real life (Meg Ryan and Russell Crowe, Elizabeth Taylor and Richard Burton) but for the most part, they tend not to.