The brain stutters or boggles at the sight or sound of taboo words, taking more processing and interfering with the normal thought train.
“The psychologist Don MacKay has done the experiment and found that people are indeed slowed down by an involuntary boggle as soon as the eyes alight on each word. The upshot is that a speaker or writer can use a taboo word to evoke an emotional response in an audience quite against their wishes. Thanks to the automatic nature of speech perception, an expletive kidnaps our attention and forces us to consider its unpleasant connotations. That makes all of us vulnerable to a mental assault whenever we are in earshot of other speakers, as if we were strapped to a chair and could be given a punch or a shock at any time.”
“In humans, the amygdala “lights up”–it shows greater metabolic activity in brain scans–when the person sees an angry face or an unpleasant word, especially a taboo word.
The response is not only emotional but involuntary. Once a word is seen or heard, we reflexively look it up in memory and respond to its meaning, including its connotation. The classic demonstration is the Stroop effect, found in every introductory psychology textbook and the topic of more than four thousand scientific papers. People are asked to look through a list of letter strings and to say aloud the color of the ink in which each one is printed.
The reason is that, among literate adults, reading a word is such an over-learned skill that it has become mandatory: You can’t will the process “off,” even when you don’t want to read the words but only pay attention to the ink. A similar thing happens with spoken words as well.”