The link between bodily cleanliness and moral purity is evident throughout the world’s cultures. Cleansing ceremonies are common in religions. Christians and Sikhs literally wash away their sins through baptism, while the act of wudu sees Muslims prepare for worship by cleaning their bodies. Our language too reveals hints of an overlap – a ‘clean conscience’ is free of guilt, while ‘dirty’ is a word for thieves and traitors.

They asked two groups of people to remember a good or bad deed from their past. Afterwards, the volunteers solved a simple word puzzle by filling in the missing letters in three incomplete words: W_ _H, SH_ _ER and S_ _P. Remarkably, those who remembered unethical deeds thought of cleaning-related words, like