The nasal and oral vowels may phonetically free-vary.
cōhāhč ‘date palm’ cōhhč
In Marrison’s [1967 : 356-7] account of Mao Naga phonology, nasalization does not find mention.
2.2.4	Diphthongs
Mao Naga has six [intramorphemic] diphthongs, two of which are diminishing or falling and four of which are rising. Marrison [loc. cit.] recognises only three, viz., ei, ei and ou, presumably diminishing.
The six intramorphemic diphthongs are "e, o, and u, i, u and e. There are five intermorphemic diphthongs : a, u, a and o; e is a rising diphthongs which may be intramorphemic or crossboundary.
2.2.4.1.	Intramorphemic Diphthongs
The diphthong {e] glides from the articulator position for the central vowel [«] to that for the front vowel [i] the former constituting the peak of sonority.
pphra ‘tear [as clothes, leaves, paper etc.] [vt]’ b ‘to close [as topic, war etc.] ibo ‘kind of plant, thick, fleshy-stalked and edible’ lop ‘she [remote]’ movupfip ‘queen’
The diphthong [o] is composed of [o] as the peak of sonority which slurs over to the higher articulatory position of [u].
mētŏŏ ‘1. paternal/maternal aunt’s/uncle’s daughter   2. sister [generic]’ pnōŏ   ‘brother [speaker : male]’
This diphthong, however, has a surprisingly in frequent occurrence, and the nonsyllabic [u] is so brief and weak that it may at times be monophthongized so that pķnōŏ ‘brother [speaker : male]’ may be, in one of its occurrences, [pķnō].
The diphthong [u], one of the four rising diphthongs, moves from the front nonsyllabic [i] to the back vowel [u], the latter being more prominent.
ģnŭ ‘to press [tr]’ ōūĭ ‘sister [generic], younger or elder [speaker : male]’ só mņhiŭ ‘to clean [tr]’
The diphthong [i], another rising diphthong moves from the non-syllabic central vowel [] to the syllabic vowel [] - the diametric reverse of the fiphthong [] as far as locus of syllabicity is concerned.
ctkhi ‘waist’
The nonsyllabic is exceedingly brief at times resulting in a monophthong :
ctli  >  ctli ‘servant’ ctvi  > ctvi ‘kind of bamboo, slender and cane-like used formaking ropes, covering wicker-work,bucket, etc.’
The diphthong [e] is a front vowel unit wherein the tongue glides from the high palatal [i] to the lower [e] the latter constituting the syllabic peak.
It occurs word-medially and -finally.
ō khěcó   ‘cough’ ōЄié   ‘gourd [generic]’ ōkhrě ‘1. phlegm 2. brain’
Like some diphthongal units discussed above, the monosyllabic at times is strikingly brief leading to a monophthong. When, in fact, it is moophthongized, the erstwhile syllabic, viz., [e] gets weaker in palatality :
ōrįcé > ōrįc   ‘sky’ [ōhié] ōrē > ōr   ‘descendant’   ōrē > ōr ‘1.seed;pip 2. bone’   nōkē > nōk   ‘branch’   mįě >  m*z   ‘make an object fly’
The diphthong [u] which has a remarkably limited occurrence, like the diphthong [o], is composed of the central vowel [], the nonsyllabic and