If the writer mentions the plot of a movie to explain a point in an essay, it is an example of allusion. An allusion is reference to an external source (a book, a movie, etc)-Irony is used to convey an opposite meaning to the literal one-Simile is used to compare two things which are not alike ( figure of speech)-Paradox is a statement that is self contradictory or absurd but might express a possible truth.