The phrase "smelt rat" is spelled with the consonant cluster "sm" at the beginning, followed by the vowel sound "eh" and the consonant cluster "lt" at the end. In IPA phonetic transcription, it would be written as /smɛlt ræt/. It is believed to have originated from the idea of a rat being cooked and therefore emitting a distinct odor. Nowadays, the phrase is often used to describe the act of suspecting someone of deceit or betrayal.