 The reason that these two had been assigned to work together was that Cobb was one of the few available police officers who knew sign language, and Tess, like the actress who portrayed her, was deaf.Dicky was usually more frustrated by Tess' attitudes than by her deafness; he also repeated what Tess said back to her to make sure that he understood it (Tess also read lips) and this allowed the audience to understand her part of the dialogue.Dicky also spoke as he signed to Tess.