The graph above plots the score of each individual phrase. For words preceded by a negation the value is inversed. E.g. happy has a value of 3 but if it is preceded by the word "not" it's value is counted as -3.
For most movies, this graph doesn't seem to show any recognizable trends.
Here we have grouped the scores of each phrase, by minute. The previous graph seemed quite random but in this one we can more clearly make out parts of the movie with a positive or negative sentiment.