I watched The Host again a few weeks ago before reading Gord Sellar's posts which examine the film in a number of contexts. If you haven't read them, and are interested in the film (or in Korean monster movies in general) then they're well worth your time, and can be found here and here.
On watching the film again, I'd noticed a bit of symmetry I that I hadn't picked up on before:
The first time we see Gang-du (played by Song Kang-ho), he is asleep at the snack booth. The first time he is seen with another character in the same shot, it's a little boy trying to steal some food.
The boy's brother then whisks him away before he gets into trouble. The next time we see the little boy and his brother, they are sneaking around a riverside park at night and breaking into a snack bar. Then they encounter the monster.
The boy is saved by Hyun-seo, and in the final scene of the movie, and the last shot in which we see Gang-du, he is again with the boy (and again, food is involved).
The other thing I noticed was that, again at the beginning, after his encounter with the boy, Gang-du is sleeping and his father is watching him and shaking his head in disbelief when suddenly a girl calls out to her father. Gang-du awakes with a start, thinking it's his daughter Hyun-seo, but he has mistaken another girl for her.
It won't be the last time he mistakes this girl for his daughter...
Unsurprisingly, he makes the same mistake twice.