Sananmuunnos ("Word transformation"), sometimes kääntösana, is a sort of verbal play in the Finnish language, similar to spoonerisms in English. Special to Finnish is a narrow phoneme inventory and vowel harmony. As Finnish is a mora-divided language, it is morae that are exchanged, not syllables (often a mora is also a syllable in a Finnish word, but not always). Also, Finnish inflectional and derivational morphology is extensive, thus applying a suffix from another word often produces a valid word. This leads to large number of possible spoonerisms. Much of practical sananmuunnos wordplay revolves around obscene double entendre expressed by spoonerism.