Literal Minded sets us straight — it’s not pronounced the way you think:
The first thing one needs to know about metathesis is that it is pronounced meTAthesis, not MEtathesis. On at least one occasion I’ve seen the word in print while I wasn’t wearing my phonology hat, pronounced it the wrong way, and thought it referred to a thesis about theses. In fact, it refers to transpositions of sounds within a word. For example, I’ve heard several people talk about “agpar scores” for newborn babies, when they mean “Apgar scores.” Or for another example, check out Semantic Compositions‘s posting on cavalry vs. Calvary.
It would be fun to build a metathesis-processer for TextMunger.