How does Clarice know “Jack Gordon” was actually the real Buffalo Bill? @Tshepang: I can't remember, but presume Starling showed a photo Mrs. Littman's face to Gumb. He didn't recognise her, and the first thing he asked was if she was "a great big fat woman". This isn't usually what people ask, and she knows the killer is interested in larger women, so this was enough to raise Starling's suspicions to find out more.