Red
The bright red of the fire engine is clearly seen from the beginning of the film. Here, the color red is a symbol of danger and a warning to anyone that the truck proceeds towards.
Books
Books are said to be dangerous by the totalitarian government, as they cause people to believe that they are better than others. Thus, books become a symbol of danger then to anyone who reads them, and a symbol of someone who is corrupted and desires to be above others.
Memorizing
The book people take it upon themselves to memorize a book so that it can be passed along without anyone attempting to destroy it forever. This is a symbol of the necessity for oral tradition so that important literature isn't just available, but a part of our culture in a meaningful way.
Breaking Down
We see one of Linda's friends begin to break down from what Montag has read. This is a symbol of the power of literature to reveal what is deep within us, but has been locked away.
Selection
Montag selects Tales of Mystery and Imagination to memorize at the end of the film. This is a symbol that he is dedicated to the cause of preserving literature and understand its meaning as deeply important to society's ability to advance.
