Why one person's erotica is another's pornography

Saoirse Ronan's new movie, Ammonite, is about Mary Anning, a shy young woman who was a pioneering fossil-hunter. Her achievements were never credited in her lifetime by male academics, but the value of her work has been rediscovered. The film also introduces an apparently fictional theme in Mary Anning's life - a same-sex relationship, which is said to be hot stuff, when Kate Winslet as Mary falls for Saoirse's character, Charlotte.