When the reversal is identical to the original, the word or phrase is called a phonetic palindrome.
This is because pronunciation in speech causes a reversed diphthong to sound different in either direction (e.g. eye [aɪ] becoming yah [jɑː]), or differently articulate a consonant depending on where it lies in a word, hence creating an imperfect reversal.
Backmasking involves not only the reversal of the sounds and order of phonemes or phones, but the reversal of the allophonic realizations of those phonemes.
Strictly speaking, a reversal of phonemes will still result in allophones appropriate for the new position; for example, if a word with a final /t/ is reversed so that the /t/ is initial, the initial /t/ will be aspirated in line with the conventional allophonic patterns of English phonology.
According to proponents of reverse speech, phonetic reversal occurs unknowingly during normal speech.