Read Japanese wordplay (Wikipedia)

Japanese wordplay relies on the nuances of the Japanese language and Japanese script for humorous effect. Japanese double entendres have a rich history in Japanese entertainment, because of the way that Japanese words can be read to have several different meanings and pronunciations (homographs). Also, several different spellings for any pronunciation and wildly differing meanings (homophones). Often replacing one spelling with another (homonyms) can give a new meaning to phrases.