This is the 16175th most frequent Korean word.
불어나는
"불어나는" means "growing" or "increasing."
In this sentence, '불어나는' describes the river water ('강물') that is swelling or increasing, showing a growing phenomenon.
불어나는 강물이 마을 근처까지 흘러들었어요.
The swelling river water flowed near the village.
Here, '불어나는' is used to describe the growing number ('숫자') of people, indicating an increase in count or volume.
불어나는 사람들의 숫자가 축제의 분위기를 고조시켰어요.
The increasing number of people heightened the festive atmosphere.
In this sentence, '불어나는' refers to the expansion or spreading of a smile ('미소'), metaphorically showing growth in a visible or figurative way.