In Chiquihuitlan Mazatec which has four tones the following minimal pairs occur: cha1 "I talk", cha2 "difficult", cha3 "his hand" cha4 "he talks". The language with the most level tones is Usila Chinantec which has five level tones and no contour tones; Trique of Chicahuaxtla has a similar system. In Copala Trique, which has a mixed system, only three level tones but five tonal registers are distinguished within the contour tones. Many other systems have only three tone levels, such as Tlapanec and Texmelucan Zapotec. Particularly common in the Oto-Pamean branch are small tonal systems with only two level tones and one contour, such as Pame and Otomi. Some others like Matlatzinca and Chichimeca Jonaz only have the level tones and no contour. In some languages, stress influences tone, for example in Pame only stressed syllables have a tonal contrast. In Mazahua the opposite occurs and all syllables except the final stressed one distinguishes tone. In Tlapanec stress is determined by the tonal contour of the words. Most languages have systems of sandhi where the tones of a word or syllable are influenced by other tones in other syllables or words. Chinantec has no Sandhi rules but Mixtec and Zapotec have elaborate systems. For Mazatec some dialects has elaborate Sandhi systems (e.g. Soyaltepec) and others have not (e.g. Huautla Mazatec). Some languages (particularly Mixtecan) also have terrace systems where some tones are "upstep" or "downstep", causing a rise or drop in pitch level for the entire tonal register in subsequent syllables. Whistled speech Several Oto-Manguean languages have systems of whistled speech, where by whistling the tonal combinations of words and phrases, information can be transmitted over distances without using words. Whistled speech is particularly common in Chinantec, Mazatec and Zapotecan languages. Proto-language Syllable structure Proto-Oto-Manguean allowed only open syllables of the structure CV (or ). Syllable initial consonant clusters are very limited, usually only sibilant-CV, CyV, CwV, nasal-CV, ChV, or are allowed. Many modern Oto-Manguean languages keep these restrictions in syllable structure but others, most notably the Oto-Pamean languages, now allow both final clusters and long syllable initial clusters. This example with three initial and three final consonants is from Northern Pame: "their houses". Phonemes The following phonemes are reconstructed for Proto-Oto-Manguean. Rensch also reconstructs four tones for Proto-Oto-Manguean. A later revised reconstruction by Terrence Kaufman adds the proto-phonemes */ts/, *//, *//, *//, *//, *//, *// and *//, and the