Both 其实(qi2 shi2) and 事实上(shi4shi2shang4) correspond to
actually or
as a matter of fact in English. It might be too long for them to say the latter.
nege, which is one of fillers in Mandarin, is a short form of 那一个(nayige), and pronounced as neige (ayi > ei).
This kind of assimilations, or palatalizations more specifically, are very common phenomena among many languages.
Day is supposed to be read as D-A-I in English, however, you pronounce it D-E-I because of assimilation (AI > EI).
(Oh, Australians pronounce
today as
to die. I guess they don't like palatalizations
)
dai in Hyundai, is pronounced as
de in Korean (ai > e).
sai in Kusai, is pronounced as
se(i) in Japanese (ai > e(i)) for informal conversation.