Co-occurrence restrictions on tones and consonants in Yuhuan Wu Chinese syllables provide a powerful illustration of the phonetic basis of phonological contrasts, with sonorant contexts allowing more tone contrasts than other contexts. Interestingly, the language also reveals that the phonetic implementation of tones depends on the phonological contrast it is involved in. Such phonetic enhancement may be the opposite of what could be expected on the basis of speech ergonomics. Moreover, the language has two tone deletion rules that exempt tones in the context with the largest number of contrasts, showing a phonological version of enhancement.