This is an instance of dramatic irony, taking into account that this figure of spech is when the implications of a situation, speech, etc, are understood by the audience but not by the characters in the play.
From person to person ( by physical contact )
The answer is: flashback.
Flashback is a transition to an earlier time in the story, interrupting the chronological order of events. It is commonly used to show a scene that explains the current events by giving the viewer additional information about the characters' past. In the excerpt about the movie I Am Legend, we have a flashback to the moment when the zombie apocalypse began.
Dramatic irony is related to a situation in which the viewers know and understand something that the characters themselves don't. A usual example is when the viewers know the police officer is talking to the killer while the police officer him/herself does not know it.
Foreshadowing is a technique in which a piece of information is given to the audience that will later on unfold into something more important, even though it seemed trivial in the beginning.
Special effects are well known. They create an illusion and may be done by diverse means. Nowadays, computer graphics are probably responsible for most of the special effects we see, along with makeup and props.
