Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is Steven Spielberg's first commercial film. It was made for TV then expanded for resease in theaters. It's typically listed as an action thriller, but basically it's a monster movie. Instead of the living creature bent on killing for no understandable we usually see in monster movies, the monster here is a truck - an old rusty beat up oil tanker that chases an ordinary man named David Mann (Dennis Weaver) for no reason but road rage because Mann passed. We see the truck's headlights in rearview mirrors looking like a monster's eyes as it tailgates Mann's red Plymouth Valiant and tries to ram him and run him off the road. It blocks the road, it slows down in front of him swerving so he can't pass, and when he tries to fall far behind it, the truck sits and waits for him. We don't ever see much of the man driving the truck. He's not important. The truck is the monster. There's a theme of lost masculinity that runs through the movie, but mostly it's just a monster truck chasing an ordinary guy for no good reason.
The snake scene
After the truck chases him for what seems like hours, Mann pulls into a small gas station to call the police. We see a sign over the gas pumps that says "Sally's Snakerama Station." On the other side of the sign it says "See the giant 8 foot rattlesnake." The budget was very low for this movie, so it's possible they used a real roadside attraction, but it would have been so cheap to make the signs and get a few cages and snakes that I suspect it was all built for the movie.
Mann asks the woman running the station where the phone is and while she checks his car, she tells him to take a look at her snakes if he has time. The snakes are in wood and wire cages on stands in the parking lot out in the sun near the phone booth. (That's a bad idea since the heat and sunlight could be deadly to the reptiles.) As Mann makes the call, suddenly the truck comes barreling towards him, crashing into the phone booth and one of the snake cages, as Mann jumps out just in time. The woman comes running, worried about her snakes. The truck circles back and smashes more cages as Mann throws a cage at him. Mann kneels down next to a rattlesnake that strikes out at him but misses, startling him as he discovers a tarantula crawling up his leg. (The woman also has a large green iguana in one of the cages and a coyote tied to a pole in her little roadside attraction.) As Mann drives away, the woman picks up a large indigo snake and continues to fret about her snakes.
Even though the woman might be taken as a comic character, a crazy old snake woman, I don't think anything about the scene is meant to be funny. Mann has tried to convince others that the truck is trying to kill him, but this is the first time anybody except Mann has witnessed it, and the first time we see that the truck is not concerned about hurting anybody else.