Characters are the dramatic centre of a film. The process of finding the right person [From the actors to the characters] and the characteristics of the fictional persona best suited to the story is a lengthy and complicated process. In the case of O Sangue, in addition to the portrayal of the characters contained in the action of the screenplay, the director often added indications on how to approach them physically and psychologically.

In scene 11, one can see how Costa highlights "the healthy young bodies", the "red faces, sweat and tense muscles" of Clara and Vicente to film the cemetery scene. This indication is accompanied in the document by a location photograph of this decor and a storyboard drawing by Rita Lopes Alves. In scene 18, we see the indication that, for Clara to be "brilliant and delicate", Vicente's body should be "pathetically abandoned" and, finally, that "each character demands to be comforted by another". These indications concern two distinct scenes in the film – the one in which Clara cuts Nino's hair and the other in which Nino sleeps on Vicente's lap, while Vicente talks to Clara, in a muted voice.