Dramatic Ignorance (n.)
Unlike in dramatic irony in which facts are not known by the characters but are known by the audience, in dramatic ignorance, authors must pretend that their characters are more ignorant than they normally would be to take into account the actual ignorance of the audience.
An example of dramatic ignorance can be found on CSI on which the following dialogue might be heard:
(Scene: Las Vegas hotel room. Sara Sidle sprays a liquid on a bed.)
Gil: What are you doing?
Sara: I’m spraying Luminol to find blood trace.
This dialogue is absurd for the characters because Gil, of course, would know what Luminol does. The dialogue is there for the benefit of the viewer, who may have actual—not dramatic—ignorance of basic forensics