What is a spoonerism?

According to the online dictionary:
the (usually) unintentional exchange of letters or syllables between two Words or even within a Word, often with comic results - especially when the result changes the speaker's intended meaning. The term is named after the 19th century clergyman and academic Rev. William Spooner William Archibald Spooner
William Archibald Spooner was a famous University of Oxford University don after whom is named a linguistic phenomenon, spoonerism....
, who was supposedly prone to this trait. Among the examples attributed to him is "you've tasted two worms" for "you've wasted two terms".

tips of the slung (slips of the tongue)

lack of pies (pack of lies) tease my ears (ease my tears)