Another truly interesting domain in which the brain confuses the literal and metaphorical is cleanliness. In a remarkable study, Chen-Bo Zhong of the University of Toronto and Katie Liljenquist of Northwestern University demonstrated how the brain has trouble distinguishing between being a dirty scoundrel and being in need of a bath. Volunteers were asked to recall either a moral or immoral act in their past. 

Afterward, as a token of appreciation, Zhong and Liljenquist offered the volunteers a choice between the gift of a pencil or of a package of antiseptic wipes. And the folks who had just wallowed in their ethical failures were more likely to go for the wipes. In the next study, volunteers were told to recall an immoral act of theirs. Afterward, subjects either did or did not have the opportunity to clean their hands. Those who were able to wash were less likely to respond to a request for help (that the experimenters had set up) that came shortly afterward. Apparently, Lady Macbeth and Pontius Pilate weren't the only ones to metaphorically absolve their sins by washing their hands.