Buy, buy! Sell, sell! Hodl, hodl! Anybody selling "E"? I'm looking to trade an "O" for an "E". This is a groat "U" – any takors? Alright, seld, "A" fer "U". Und ne rotarns noither.

Just a normal day at the Vowel Exchange.

Explanation: during the Great Vowel Shift, English pronunciation changed dramatically. Vowels went from the Latin vowel sounds to the modern sounds we use today. Think of the "a" sound in "lathe", or Mr Fonzie's iconic "ayy". In Classical Latin and Middle English, this same sound would be written as a long "e", but in Modern English we now use the long "a". Other vowels exchanged sounds similarly.

In this joke, I am imagining what the Great Vowel Shift would have been like if, instead of happening in the mouths of peasants in the fifteenth century, it had occurred inside a stock exchange on Wall Street.

Inside the stock exchange, the narrator is selling vowels, and trading them for other vowels. The really fun part is that when the narrator sells one vowel, his own speech changes to reflect the trade that has taken place. After trading an "O" for an "E", the narrator wishes to say "great", but it instead comes out as "groat". This vowel transliteration produces rather amusing results if you read it phonetically: I think it takes on a kind of Yorkshire accent, but of course I know nothing of phonology.