People with ASD frequently do not understand figurative language such as sarcasm, metaphors, irony, proverbs and quite often humor in general. The phrase “he’s pulling your leg” as another way of saying “he’s kidding”, would mean something very different to someone on the spectrum, unless they’ve memorized this- a process much like learning a word in another language.
Because children with ASD also have difficulties with homographs, or words spelled the same way, such as bass meaning either a deep tone or a fish, and homophones, or words that sound the same, as in sees / seas / seize, unless they are able to see the word in print, it is suggested that one verbal word or phrase is stored in memory as one internal image (Happé, 1997).
Even high functioning autistics (HFAs) with above average intelligence struggle with proverbs. The difficulty lies not only in finding a commonality between two unrelated concepts, but then having to interpret the meaning of the relationship in order to understand a proverb (Chahboun, Vulchanov, Saldaña, Eshuis, & Vulchanova, 2016).
Chahboun, S., Vulchanov, V., Saldaña, D., Eshuis, H., Vulchanova, M. (2016). Can you play with fire and not hurt yourself? A comparative study in figurative language comprehension with individuals with and without autism spectrum disorder. PLoS ONE, 11(12): e0168571. Doi:10.1371/journal.pone.0168571
Happé, F. G. E. (1997). Central coherence and theory of mind in autism: Reading homographs in context. British Journal of Developmental Psychology, 15, 1-12.