We all seem to have tiny little mental blocks, micro-aphasias, things that we, try as dammit, cannot learn. My mother couldn’t remember the word “volcano”—she was a perfectly fluent native speaker of English, with no other language difficulties, but whenever she came to that word it was always “one of those mountain-things with smoke coming out of the top” or similar, followed by several seconds until the word came to her. I have a block on the ideas of “horizontal” and “vertical”. Whenever I read these, I feel my mind blurring; I know which two concepts they map on to, but for a second or two (which feels like an eternity in the usual flow of thought) I cannot fluently map the words onto the concepts. Usually I break the fog by making a gesture with my fingers—somehow, this change of mode (moving my fingers from left to right strongly associates with the word “horizontal”) dispels the confusion, it must trigger a different part of my memory associations. Quite where these odd little blocks come from—and, why we can’t just learn them away—is fascinating.