Celinese not only has initial mutation, but internal mutation too. The latter is often caused when creating compound words or adding morphemes to the beginning of words. As a rule of thumb, it is words and modifiers that end in vowels or voiced consonants that bring about these changes. When internal mutation occurs, there is no ecliptic form - instead, the consonant is written like its mutated sound.
Interestingly, this phenomenon was once proscribed by traditional grammarians and lexicographers who believed that internal mutation was purely a spoken phenomenon and should not be denoted in writing - the 990 Lexicographers' meeting finally put paid to this notion and one of their key reforms was to recommend internal mutation be denoted in all words. For the time being, pre-reform, non-mutated forms like cêthoní (to dine [together]) coëxist with cêðoní, which reflects the current pronunciation. Here are a few common prefixes that cause internal mutation.
Cé, cê: Literally deriving from cé, with, this prefix can be compared to co(n)- in English, but is used much more frequently, because it can be attached to any word to denote a mutual activity or byproduct of an action: thigrí (pause for thought) becomes cêðigrí (deliberate, confer together); whilst tinyor (sound) becomes cêdinyor (connotation) and ceðorí (sort, arrange) becomes cêgeðorí (coördinate.)
Lo: From lo (to), often used to communicate causation, though how lo- forms differ from the original infinitive can be complex. Polí (to be able to) becomes nobolí (facilitate); ponthí (assure) becomes lobonthí (settle, guarantee); flyní (ask) becomes lowlyní (put into question); thoní (eat) becomes loðoní (feed, nurture).
Internal mutation is also often triggered by compounding - if the last consonant in a compound is a voiced plosive or, in many cases, any voiced consonant, then it voices (and often assimilates) any voiceless consonant that directly follows - to take two examples, when one compounds cyg- (blind, from cygeg) with cyroir (school), or neb- (big, from nebor) with tír (land), one gets cyg(g)yroir (school for the blind) and nebdír (continent).