Japanese wordplay relies on the nuances of the Japanese language and Japanese script for humorous effect. Double entendres have a rich history in Japanese entertainment (such as in kakekotoba) due to the language's large number of homographs (different meanings for a given spelling) and homophones (different meanings for a given pronunciation). Kakekotoba or "pivot words" are an early form of Japanese wordplay used in waka poetry, wherein some words represent two homonyms. The presence of multiple meanings within these words allowed poets to impart more meaning into fewer words. Goroawase is an especially common form of Japanese wordplay, wherein homophonous words are associated with a given series of letters, numbers or symbols, in order to associate a new meaning with that series. The new words can be used to express a superstition about certain letters or numbers. More commonly, however, goroawase is used as a mnemonic technique, especially in the memorization of numbers such as dates in history, scientific constants and phone numbers. Numeric substitution Every digit has a set of possible phonetic values, due to the variety of valid Japanese kanji readings (kun'yomi and on'yomi) and English-origin pronunciations for numbers in Japanese. Often, readings are created by taking the standard reading and retaining only the first syllable (for example, roku becomes ro). Goroawase substitutions are well known as mnemonics, notably in the selection of memorable telephone numbers used by companies and the memorization of numbers such as years in the study of history. Mnemonics are formed by selecting a suitable reading for a given number; the tables below list the most common readings, though other readings are also possible. Variants of readings may be produced through consonant voicing (via a dakuten or handakuten) or gemination (via a sokuon), vowel lengthening (via a chōonpu), or the insertion of the nasal mora n (). Examples As mnemonics 1492, the year of discovery of America, can be read as "i-yo-ku-ni" and appended with "ga mieta" to form the phrase "Alright! I can see land!" (). Additionally, "i-yo-ku-ni" itself could simply be interpreted as "alright, country" (). The alternative reading "i-shi-ku-ni" is not typically associated with a particular meaning, but is used to memorize the year. 23564, the length of a sidereal day (23 hours, 56 minutes, 4 seconds), can be read as "ni-san-go-ro-shi", which sounds similar to "nii-san koroshi" () or in English, "killing one's older brother". 3.14159265, the first nine digits