Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a beautiful Oscar-nominated animated film in which every frame is made from an oil painting on canvas simulating the technique of Vincent van Gogh. The animation was made from film of live actors and then each frame of the film was painted. This is why some of the actors faces are very recognizable, as well as their voices, including Saoirse Ronan and Chris O'Dowd. But unfortunately for us, the snake scene is shown as a flashback, and flashbacks, in this brilliantly-colored film, are in boring black and white. Sad emoji. But they still were painted in oils on canvas. They are more like Van Gogh's early less colorful and more realist period.
The flashback with the snake shows Rene, one of the teenage rich boys who is visiting the countryside town where van Gogh is painting. (This is after Vincent cut off his ear and recovered in an asylum.) Rene sneaks up on van Gogh and puts a snake in his paint box. When van Gogh sees the snake, he falls over on his side in fear. The kid laughs wickedly. At the end of the movie we learn that Rene is the same boy who was waving around a gun and is most likely the person who accidentally shot van Gogh, causing him to die two days later. Van Gogh's death is usually considered a suicide, but some experts believe he was shot by someone else.