I mentioned my own theory in some other thread--can't remember which one, and it doesn't seem to be coming up with the Google search.

Essentially, it was that you could be typing, and anything could interrupt the train of thought, but since the brain continues to play the sound of the word in your head, you "hear" the sound and type what you hear instead of what you mean, then possibly recover your train of thought and continue (either that or notice the mistake right there).

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info