A pun (or paronomasia) is a phrase that deliberately exploits confusion between similar words for rhetorical effect, whether humorous or serious. A pun may also exploit confusion between two senses of the same written or spoken word, due to homophony, homography, homonymy, polysemy, or metaphorical usage. For example, in the phrase, "There is nothing punny about bad puns", the pun takes place in the deliberate confusion of the implied word "funny" by the substitution of the word "punny", a heterophone of "funny". By definition, puns must be deliberate; an involuntary substitution of similar words is called a malapropism.