Frequently, when the question does not ask for understanding of spoken language, there still would appear the loudspeaker icon in blue at the top of the discussion page, and this would again frequently have one pronounciation of the word. Always worthwhile testing.
Unfortunately the pronounciation changes from case to case with some rules, which makes Irish pronounciation almost as hard to grasp, as English pronounciation. wear, tear, great ... (BTW would you pronouce the great Sligoman's name W B Yeats with an "a" or with an "e"?)
I'm pretty sure that's because in both "chugainn" and "culaith" the c is modified by the broad vowel "u". I'm not sure if "ch" is any different from "c", but it seems like you're getting tripped up by the way broad and slender vowels change a consonant's pronunciation. A O and U are broad, E and I are slender.