Earlier quoted context omitted.
Copyright law considers the importance of a sample to the work as a whole, in addition to just the size. Any arbitrary three-word phrase from the middle of a script is probably not copyright infringement. The most memorable line from the entire movie probably is. Related: The Supreme Court ruled that excerpting a single paragraph from a 454-page book can be copyright infringement. The book was Gerald Ford's memoirs,…
The amount and substantiality of the copied portion to the work as a whole is one of the factors for fair use, an affirmative defense. Whether a work in question is even eligible for protection at all is a distinct legal question.
The question in play is how much of of the copyrighted work may be reproduced before it is infringement.