Rhyme-as-reason effect
The rhyme-as-reason effect, or Eaton–Rosen phenomenon, is a cognitive bias whereupon a saying or aphorism is judged as more accurate or truthful when it is rewritten to rhyme. In experiments, subjects judged variations of sayings which did and did not rhyme, and tended to evaluate those that rhymed as more truthful (controlled for meaning). For example, the saying "What sobriety conceals, alcohol reveals" was judged more accurate on average than: "What sobriety conceals, alcohol unmasks", sampling across separate groups of subjects (who each assessed the accuracy of only one of these statements). The effect could be caused by the Keats heuristic, according to which a statement's truth is evaluated according to aesthetic qualities; or the fluency heuristic, according to which things could be preferred due to their ease of cognitive processing. Studies and theories 
'Birds of a Feather Flock Conjointly (? ): Rhyme as Reason in Aphorisms' is a seminal study that explores the role of rhyme in the creation and perception of aphorisms. It is conclusive that the use of rhyme in aphorisms may serve as a heuristic, making the aphorism more memorable and persuasive. Study on effectiveness of a "chiastic structure", as a type of linguistic structure that change the phrasing in an aesthetic manner, shows its effect in increasing the perceived accuracy of statements. The higher veracity is arguably due to the aesthetically pleasing and memorable nature of chiastic structure, creating a greater perceived coherence and truth in the statement. In the study of ‘A reason to rhyme: Phonological and semantic influences on lexical access’, those who were influenced by the rhyme prime in the verbal sentence completion task with a missing word were faster than those influenced by non-rhymed priming. This study indicated the role surface feature such as rhyme plays in lexical access, as well as higher memorability and acceptance of rhymed saying . Furthermore, people will frequently agree to a message based on heuristics like "reputable sources tend to make true assertions" or "familiar sayings tend to be believable" when they lack the expertise or desire to thoroughly assess the message. The influences on people's judgements are usually unknown in their perception,  according to documentation. It means under some conditions people may rely on a generalization that equates a message's ease of rhyming with its veracity. Keats Heuristics 
The Keats heuristics illustrated how poetic structure can influence the perception of line of words, which is the broad concept of this effect. The name 'Keats' is in reference to John Keats' statement "Beauty is truth, truth beauty - that is all / Ye know on earth, and all ye need to know," which is a rhyming aphorism that has become famous for its poetic beauty and philosophical depth. This heuristics means people may partially biases their assessments of a statement's veracity on its aesthetic attributes. The results of the experiments showed that participants consistently assessed the rhyming aphorisms as more agreeable and truthful than the non-rhyming aphorisms, even when the content of the two sayings were identical, or the rhyming content lacks logical validity. The effect is the strongest when there is little distinction between poetic qualities such as fluency derived from rhyming and its truthfulness from semantic content. Hence, it could be infer that the presence of rhyme within the poetic structure of an aphorism act as a cue to deeper meaning, prefer rhyme as 'pleasurable aesthetics', the rhyme as component creates a sense of unity and coherence, increases its appeal to be repeat and remember. It is often in combination with fluency heuristics to explain this cognitive bias. Fluency Heuristics 
Fluency heuristic is defined as  'when one of the objects is more fluently retrieved, then it could be infer that this object has the higher value with respect to criterion'. According to this heuristic, the value placed on a phrase is linked to how quickly it is processed. The rhymed sayings are usually with higher fluency for retrieval, correspondingly, the higher value would be assumed. People don't always make reasonable decisions based on declarative knowledge, and the ease of processing may lead to more positive evaluations of the aphorism. Non-fluent processed stimuli have a psychologically more remote feeling than fluently processed stimuli, which causes them to be viewed as being further away and in a more abstract perspective. The most appealing choice is the most fluent, hence, the simplest to process. For example, cities with names that are processed smoothly appear closer than those with names that are processed without a smooth fluency. Criticisms 
Although many well-known and frequently used aphorisms rhyme (for example, "A friend in need is a friend indeed"); participants may have chosen them because they subconsciously connected them with the condensed wisdom of the centuries, rather than the rhyming properties. And the perceived credibility of rhymes versus non-rhymes did not differ significantly according to the questionnaire that put the emphasis on the content features of the social advertising slogans. Furthermore, 'rhyme as reason effect' is also dependent on the level of allocated attention on the content. When participants in the experiments were deliberately asked to pay more attention to identify the difference between poetic structure and the semantic content in the rhyme, the greater perceived truth illustrated by this effect were massively reduced. Similar effects were also shown when people have pre-existing opinions on the aphorisms. On the other hand, the extent of how frequently and lately relevant stimuli have been exposed correlates strongly with retrieval fluency, which links to fluency heuristics. It could be infer that this effect is a result of enhanced processing fluency, often produced from the repeated exposure or factors in stimulus environment such as fluency manipulations. These factors thus creating greater familiarity for recall, rather than the extent of rhyming. see also : illusion truth effect

Real world implications 
It was found that people strongly preferred rhyming slogans over their non-rhyming equivalents. Rhymes were assessed as being more endearing, unique, more memorable and convincing, hence it's suitable for advertising. But the quality of the rhymes was also important as it determines the extent of the trustworthiness. In order for customers to accept the claims automatically and without slow and in-depth analysis, the marketing message should be as fluent as possible. This demonstrates the application of this effect on a day-to-day basis and further emphasizes how prevalent “aesthetic” is in our life, affecting our choice and perception. This phonological resemblance found in a nursery rhyme may encourage young toddlers to pay more attention to phonological than to semantic elements, with a negative effect it has on children's short term memory retention. It is either because phonetic processing creates relatively fleeting memory traces , or because it does not evoke "transfer appropriate" information to the long term memory, which was difficult to resemble the sentences' meaning. This 'rhyme as reason' may be a rather superficial type of processing, which is inappropriate for semantic comprehension in children's cognitive development. In the court, rhyme made it more likely for jurors to practice, retain, and ultimately implement attorney's instruction, this manipulation could bias the results. These findings have implications for the use of language in persuasive communication and may also shed light on the role of language in shaping our perception of the world. References 

Cognitive biases