The four-letter words in this article are neither offensive nor vulgar, and for the most part do not relate to excrement or copulation. This disavowal is made up front so that you won't waste time looking for the nonexistent X-rated words.
"Foursquares:Four Letter Word Fun,"
Word Ways: Vol. 25
, Article 3.
Available at: http://digitalcommons.butler.edu/wordways/vol25/iss4/3