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 quirky adventure movie with a child protagonist made by Jean-Pierre Jeunet whose whimsical movies (such as Amelie) are worth watching for their production design alone. It's mostly about a boy running away from home to hop a train and travel accross the country to accept an award for his invention, but it also includes a short scene with a rattlesnake.
T. S. Spivet is a 10-year-old boy prodigy who lives on a ranch in Montana where he makes maps and designs scientific inventions. His mother is a naturalist, obsessed with studying insects, and his father is a cowboy who wishes he was alive in the days of the old west. After his fraternal twin brother dies in a gun accident, T. S. feels guilty and worries that his father blames him for the loss of his favorite son. The father takes T. S. in his truck to do some work on the ranch when they stop to untangle a goat named Stinky from some barbed wire. T. S. is helping the goat when he hears a rattling sound and looks up to see a rattlesnake staring at him. He freezes, unable to do anything when he hears a gunshot and sees the snake drop. His father leaves the truck to shoot the snake then asks him if he was planning on "...kissing that poison rope." Unfortunately, T. S. is confused by the meaning of his father's action, which foreshadows another action in the future where he reacts violently so save T. S.
When I first saw the scene, I thought it was badly done: the snake is entirely CGI and looks like a cartoon monster; the father shot the snake in T. S.'s direction, instead of walking up to T. S. and shooting away from him; and of course there was no real reason to shoot the snake when it was so far from the boy that he could have just backed away. But the more I think about it, the more it works just fine. We see the snake through T. S.'s eyes. To him it appears as a huge monster threatening his life so he freezes not knowing what to do, thinking he's in more danger than he really is. That's in character for him. And the father shoots the snake just like the old west movie cowboys he idolizes always do. And maybe he was worried that the snake would bite the goat so he couldn't just leave it there alive. I still think he should not have shot in the direction of T.S., but maybe he did that so the boy would see what he was doing and not make any sudden moves.