•The feature rhotacization describes an auditory property, the r-coloring, of a vowel. •In most forms of American English, there are both stressed and unstressed rhotacized vowels. The transcription for the phrase "my sister's bird" in most forms of American English would be [maI 'sIstÔz 'bÎÕùd]. •X-ray studies of speech have shown that in both these ways of producing a rhotacized quality there is usually a constriction in the pharynx caused by retraction of the part of the tongue below the epiglottis.