Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This was nominated for a best picture Oscar. It's about a family from California that re-locates to Arkansas in the 1980s to work in a chicken hatchery and start a family farm. To help them with their young boy and girl, the bring grandmother Soonja from Korea (played by Yuh-Jung Youn, who won an Oscar for her performance.) One day Soonja and the children walk to a creek near the farm where she finds a good place to plant minari, an edible plant. The girl warns her that the area is not safe because of snakes. When I heard that, I thought we might see a snake there later, and we do.
We see Soonja and the boy at the creek, where she is picking some of the minari she planted. He sees a snake crawling on a tree branch and calls to his grandmother, then throws a rock at it. She scolds him to stop because the snake might crawl away and hide and it's better to keep the snake where they can see it because things that hide are more dangerous. Then we see him drop a rock at his feet. This was a lesson for the boy that had to come up again later in the film.
After she has a stroke, we see Soonja lying in bed and pointing in fear at her dresser. She tells the girl to leave it alone because it will hide. We don't know what "it" is, but based on her lesson for the boy, it's something dangerous. Then the family's fanatical Christian farmhand performs an exorcism at the dresser to cast out something evil. We never find out what she is referring to, but I don't think it was another snake.
The film was based on the life of the writer/director Lee Isaac Chung, including the snake scene. According to IMDB he said: "I remembered the creek where I threw rocks at snakes while my grandmother planted a Korean vegetable that grew without effort."
The snake we see is a black rat snake, a species found in Arkansas and also in Oklahoma where the movie was filmed.