Literary Device -- Flashback

Flashback => A scene that has happened before what is taking currently taking place in the story (or play).  

In the P. Martin story, one flashback is introduced by P. Martin remembering what had happened the night he was doing his homework about Brazil.  The phrase, Last week . . . , is like a trumpet call -- or an alarm clock -- announcing the memory.    

One way to notice if the writer has used a flashback is to look at a change in the verb tense.  Now, it gets tricky:  if the story is moving along in the past tense (something that happened in the past) and then you, the reader, notice that the verb tense has changed to past perfect (something that has already happened before the event being described) chances are you are reading a memory (or flashback) a character is recalling.  

The same holds true if the story is written in present tense (meaning the action is happening while you, the reader, are reading it) and then switches to past tense.

Whew -- that's a lot of information all at once!  (More about verb tenses later)

Another way a writer creates a flashback is through the use of a transitional phrase, such a "last week" or "yesterday."  That alerts the reader to a change in time, without using an immediate change in the verb tense.  Notice that the writing is still in past tense, but then switches to the past perfect.  Think of it as the writer doing a stretching exercise before running.