Every word has a total of 2 vowels. The 2 vowels are different. They can be anywhere in the word except adjacent to each other. In the word pairs listed, the vowels under consideration are supplemented by like consonants in the same positions in each word.
"Vowel To Vowel Replacements,"
Word Ways: Vol. 51
, Article 11.
Available at: https://digitalcommons.butler.edu/wordways/vol51/iss2/11