Tom Jacobs of Miller-McCune reports on more evidence for the biological basis of metaphor—and the surprising effect physical experience can have on our beliefs and opinions. In ‘Taste Buds Reflect Feelings of Moral Disgust‘, Jacobs describes experiments at the University of Illinois in which self-described Christians more often described a beverage as ‘disgusting’ following exposure to the incompatible belief systems of atheism or Islam.

Participants tasted a drink and rated its ‘disgustingness’. Then they read a passage from the Koran, an excerpt from Richard Dawkins’ The God Delusion or the preface to Merriam-Webster’s Dictionary and performed another taste test, this time with a drink they were told was different from the first one but was actually identical to it. Participants “showed an increased disgust response following contact with rejected religious beliefs (i.e., Islam and atheism), but not a neutral text,” Jacobs quotes from the study. The researchers’ preliminary conclusion: Contact with distasteful beliefs really does leave a bad taste in our mouths.

The feeling of physical disgust likely evolved as a mechanism for avoiding things (rotten food, decaying bodies) that could harm us. Intellectual disgust likely evolved as a mechanism for avoiding ideas that could do the same, but the experience and expression of intellectual disgust metaphorically piggybacked on those of physical disgust. The researchers noted the disgust effect was eliminated when participants washed their hands after reading the offending passages, a demonstration of the ‘Macbeth effect’ in which a perceived threat to moral purity can prompt actual physical cleansing, just as in Shakespeare’s play Lady Macbeth tries in vain to scrub the stain of murder from her hands. Our bodies dictate our beliefs more than we care to admit. There, I’ve said it. Now I’m going to wash my mouth out with soap.