In a thesis on multi-word units in dictionaries (page 16; pdf page 38), the researcher touches upon phonological idioms, using the definition:
a fixed expression which has an oddity of pronunciation
Then he mentions the following examples, noting that the oddity is in the capitalized predicates:
the penny DROPPED
the mind BOGGLES
the plot THICKENS
where the shoe PINCHES
I don’t really get the oddity in those pronunciations. Could you please further explain the idea?
I have done some research on Google, but all I found was that phonological idioms are in fact mostly common among children since they tend to mispronounce the words.