Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This movie lumps all Mexican Americans and Mexicans together using the term "Mexicans" so I will do the same here even though it might be considered offensive. (Don't complain to me, it's the title of the movie.) The movie tells us that a third of the population of California, 60 percent of construction workers, and even 50 percent of the Border Patrol are Mexicans. It shows us what would happen if all of the Mexicans living in California disappeared - tortilla machines would keep running wasting perfectly good tortillas, fast food restaurants would have nobody to give you fries with that, leaf blowers would bounce around on the sidewalks with nobody to hold them, low rider cars would bounce their hydrolics up and down on the street without a driver, restaurants would have no dishwashers, bus boys, or parking valets, privileged white people would freak out because they would have to cook their own breakfasts paint their own houses and take out their own garbage, Border Patrol workers would start looking for new jobs, and all agricultural crops would rot because non-Mexicans are too stupid to be able to pick fruit. It's a total farce with lots that cannot be taken literally, a satire with some good social commentary and comedy along with a healthy dose of schmaltz, or whatever the Mexican food equivalent is. (Flan?) My favorite scene is when all the Mexicans finally return and the Border Patrol officers have a huge celebration next to the border fence.
The snake scene is as stupid as most movie snake scenes. Once again a rattlesnake is shown as a lethal weapon just waiting to kill somebody, with the additional message to fit the theme of this movie that if all the Mexicans disappeared, there would be nobody to shoot rattlesnakes and save our children's lives. In the scene, a man who supports a racist group that opposes illegal immigration and his more tolerant father drive up to the father's farmhouse where they see a Mexican worker named Jose, aiming a rifle and firing towards the younger man's young son. Then we see Jose pick up a huge Western Diamond-backed Rattlesnake (which is not native to the San Diego area where the movie takes place and was filmed.) Everybody agrees that it is a really big snake (size is always important to men, of course - who wants to kill a wimpy little snake?) and the farmer tells the kid that Jose saved his life. The kid thanks him in Spanish (which bothers the father) and Jose tells the kid that he will make him a belt from the snake. Jose then carries the snake away. As always, I wanted to scream at the stupidity of seeing another senseless snake killing on screen. It only continues to promote the unnecessary killing of all snakes, but what's the point of complaining when even the governor of the state, Jerry Brown, in 2015 posted a picture of himself holding a rattlesnake that he killed for absolutely no good reason. Somebody needs to make a film titled "A Day Without Rattlesnakes." I'll be the only guy in the theater while everybody else celebrates.
We never see the snake alive before it is shot. The snake Jose is carrying is a real dead rattlesnake, though we don't know if they killed it just for the movie, but they probably did since there is no way they could have found a dead one around San Diego. Or maybe somebody sells dead snakes for the movies. There is a disclaimer at the end which says that no Mexicans were harmed in the making of this movie (continuing the satire about Mexicans being taken for granted as if they were animals) but there was no disclaimer about not harming animals.