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 big budget re-make of a 1974 car chase independent movie. Nicholas Cage plays a retired car thief who is forced to save his brother's life by putting together a crew to steal 50 particular kinds of cars in a couple of days. He assembles a crew of car thieves to help him. The cast is good (though Anjelina Jolie is wasted), the car chases are good, the plot, not so much. This remake uses professional actors and has a plot, unlike the original, which was written and directed and stars a stunt driver who just wanted to crash a lot of cars. And he succeeded.
The snake scene is a comic interlude, with a brief chase and car crash. Two car thieves steal a Hummer parked in a garage that has the vanity license plate "Snake." As they are driving the monster truck out of the garage, a large Boa Constrictor starts to crawl up from the floor between the legs of the passenger. He screams and screams and screams that there's a snake in the truck and it's crawling up his butt, telling the driver to help him. Two plainclothes cops are searching for the thieves, and when the passenger's screaming causes the driver to scrape the side of the Hummer on the garage wall, they are alerted to the car thieves and follow them closely. The Hummer driver rams them and pushes them off the ramp. They crash onto a level below them. Then one of the thieves throws the snake onto the roof of the cops' car. I'm guessing it was the driver since the passenger was such a baby. The cops are stunned from the crash, and they make surprised faces when they hear the thud of the snake landing on their roof.
The snake we see is a harmless Boa Constrictor. Why did the idiot Hummer owner keep his snake in his truck? He deserved to lose both of them.
FYI, the original did not have a snake scene, but it did have a scene in which one of the car thieves breaks into a car to find a tiger in the back seat. A harmless snake loose in a car wouldn't scare me, but I'd lose my mind if I saw a tiger!