Four-letter words are famously well connected to each other. Fewer than one per cent of words connect to no other, whereas over 70 per cent in each of the four possible positions-on average, there are 23 neighbours for each word. For our present purpose, note that more than three-quarters are heterograms. This means that Connoisseur's Ladders (those with sequential replacement between heterograms, plus a relationship between the first and last words) become commonplace. On the other hand, the number of such ladders is restricted by the relatively small number (fewer than 20,000) of four-letter words available.
"Four-Letter Super Connoisseur's Ladders,"
Word Ways: Vol. 34
, Article 14.
Available at: http://digitalcommons.butler.edu/wordways/vol34/iss2/14