slightly labialized as well. In some rhotic accents, such as General American, when not followed by a vowel is realized as an r-coloring of the preceding vowel or its coda: nurse , butter . The distinctions between the nasals are neutralized in some environments. For example, before a final , or there is nearly always only one nasal sound that can appear in each case: , or respectively (as in the words limp, lint, link – note that the n of link is pronounced ). This effect can even occur across syllable or word boundaries, particularly in stressed syllables: synchrony is pronounced whereas synchronic may be pronounced either as or as . For other possible syllable-final combinations, see in the Phonotactics section below. Obstruents In most dialects, the fortis stops and affricate have various different allophones, and are distinguished from the lenis stops and affricate by several phonetic features. The allophones of the fortes include: aspirated when they occur in the onset of a stressed syllable, as in potato. In clusters involving a following liquid, the aspiration typically manifests as the devoicing of this liquid. These sounds are unaspirated after within the same syllable, as in stan, span, scan, and at the ends of syllables, as in mat, map, mac. The voiceless fricatives are always unaspirated, but a notable exception to this are English-speaking areas of Wales, where they are often aspirated. In many accents of English, fortis stops are glottalized in some positions. This may be heard either as a glottal stop preceding the oral closure ("pre-glottalization" or "glottal reinforcement") or as a substitution of the glottal stop for the oral stop (glottal replacement). can only be pre-glottalized. Pre-glottalization normally occurs in British and American English when the fortis consonant phoneme is followed by another consonant or when the consonant is in final position. Thus football and catching are often pronounced and , respectively. Glottal replacement often happens in cases such as those just given, so that football is frequently pronounced . In addition, however, glottal replacement is increasingly common in British English when occurs between vowels if the preceding vowel is stressed; thus better is often pronounced by younger speakers as . Such t-glottalization also occurs in many British regional accents, including Cockney, where it can also occur at the end of words, and where and are sometimes treated the same way. Among stops, both fortes and lenes: