Aristotle wrote in the Poetics "Metaphor consists in giving the thing a name that belongs to something else. The greatest thing by far is to be master of the metaphor" (Ross, 1952). Comprehension of metaphor and simile can be very difficult for students who are unprepared to process language at a non-literal level. This is often the case because students are typically exposed to comprehension instruction that has been directed at deriving only literal meaning from the text. On the other hand, some speakers or writers do not intend language to be interpreted literally.
Fawson, P. C., & Reutzel, D. R. (1994). Comprehending Metaphor: Using a Salient Characteristic Analysis Technique (SCAT). Reading Horizons, 34 (4). Retrieved from http://scholarworks.wmich.edu/reading_horizons/vol34/iss4/6