<p><br /> Amanda Seyfried's revealed the biggest peril of being a Hollywood film star - the screen kiss.<br /> </p><p><br /> "It's not fun when you're with somebody," the 24-year-old said.<br /> </p><p><br /> The actress is dating her Mamma Mia co-star Dominic Cooper and while filming her new movie Letters to Juliet kept him up-to-date on her characters love-life.<br /> </p><p><br /> She said: "If either of us find out that we've been kissing our significant screen other and we find out a couple of days later, that it happened like a couple of days before, we get mad! Because if it's happening you tell the person."<br /> </p><p><br /> Seyfried stars alongside legendary actress Vanessa Redgrave in new romantic film Letters to Juliet. It is released Wednesday 9 June.<br /> </p>
