Spoonerism

A spoonerism is an error in speech or deliberate play on words in which corresponding consonants, vowels, or morphemes are switched (see metathesis) between two words in a phrase.

An example is saying "The Lord is a shoving leopard" instead of "The Lord is a loving shepherd." While spoonerisms are commonly heard as slips of the tongue resulting from unintentionally getting one's words in a tangle, they can also be used intentionally as a play on words.