Neurological experts who are fans of the show have speculated that Nairn's character on
Game of Thrones (2011) suffers from Expressive Aphasia, in which sufferers can be fully literate, and know & understand everything said to them, but can only speak as little as one or two words, either due to a stroke, aneurysm, head trauma, or other neurological damage to a part of the brain known as Broca's Area (an alternate term for the condition is Broca's Aphasia). Ironically, considering he only repeats "Hodor" on screen, Nairn is known for being quite verbose off-screen.