Sis Hyeri does not have 10 lines sit down.
The head voice part isn't her, it's Sojin mostly, and Hyeri sings like the first two words of every phrase. Furthermore, Sojin sings it when they perform, and Hyeri only actually opens her mouth for for the second
"
nae choge jjillinabwa
heoreul jjireunikka neogsi naga"'
I'm not saying her voice isn't present in the studio version cause it is, her part is just buried underneath backing vocals. Though usually what I've noticed producers do is they have the members who aren't main vocalists do a lot of the head voice-y, in-between parts that no one really registers while listening to the song, or backing vocals for the main vocalists.
out of nothing, especially in girlgroups? 
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