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 horror/thriller about Lisa and Wade, an American couple who go to Australia on vacation, make some bad decisions, then get lost in the middle of nowhere, which Australians call the Outback. It's supposed to be based on a true story, if you believe the advertising. "Dumb and Dumber conquer the outback" is one description I've read, and that's fairly accurate, mostly because they unwisely rely on technology to guide them (the GPS on a smart phone) instead of common sense.
I assumed there would be a snake in the movie. I watched it because I like the Australian outback, having spent a few weeks camping there hunting for snakes and lizards, but mostly because I was suckered in by the various posters I'd seen. All of these posters show a woman on the ground with a snake raised up in her face or on the ground behind her. One poster also shows a scorpion in front of her. But this snake scene does not appear anywhere in the movie, and neither does the scorpion scene. Each poster shows a different kind of snake, and none of these snakes is the snake we do eventually see in the movie - the Black-headed Python that we saw in the brochure photo. So the posters are false advertising, but since there were two snake scenes in the movie plus the set-up I just described, the worst I can say is that the posters are simply the typical sort of bait-and-switch we see in many movie posters and trailers.
They rent a car and drive straight to a beach north of Sydney where Wade gets stung by a venomous jellyfish, so Lisa recommends that they drive to Uluru (that huge red rock in the outback you've seen in many pictures) telling Wade: "If you've seen one beach, you've seen them all, but there's only one outback." He programs the GPS to take them there and their fight for survival begins. Google tells me that the drive from Sydney, where their plane landed, to Ulluru takes 30 hours. Most people would fly there, or at least take their time and enjoy the scenery, but not these geniuses.
Earlier we heard Lisa reading a tourist brochure that explains some facts about Australian wildlife, such as that 21 out of the 25 of the world's deadliest snakes call Australia home, and that the deadliest is the Black-headed Taipan which is attracted to fear. We see a picture of a snake with a black head. Wade responds: "Welcome to Australia: a giant death trap." This was such obvious foreshadowing and such an obvious set-up for a future snake scene that I got excited, even though I knew that there is no such snake as the Black-headed Taipan, and that the snake in the picture we see is actually a Black-headed Python, a harmless Australian snake. (That's OK because Taipans really are the most deadly Australian snakes and I certainly don't expect the filmmakers to use any kind of deadly snake around the actors or crew.)
The first snake scene happens after their GPS keeps re-routing them onto isolated dirt roads in the outback and Wade finally stops the car to go take a pee. On the ground at his feet he sees a snake and freaks out then kicks dirt at the snake. Lisa asks him what's happening and he tells her: "There's a snake. Get back in the car" but she gets out anyway and asks him if it was big. He tells her it was enormous ... and so was the snake. I was not even a little bit surprised that Wade would make a lame penis joke. You can't blame him. She totally set him up.
The last snake scene happens at the very end. Six days after they got stranded in the outback, unable to find their car, with no food, water or phone service, forced to sleep on the ground listening to wild Dingos howling, after Lisa is stung by a scorpion which makes her pass out, after they are force to drink urine (which led someone to title the movie "Urine the Outback", we finally see Lisa back inside the car, which now has a dead battery, and is parked in the same place where we saw the first snake. As she pulls out the case holding the wedding ring with which Wade proposed to her on the plane, she sees a snake on the floor of the car. Instead of panicking she just says "Oh my". She must have remembered that Taipans are attracted to fear. (That is so ridiculous it made me laugh when I first heard it.) But she stays calm as the snake crawls up her leg and arm, onto her lap, over her crotch and towards her face. Eventually she decides to make a deal with the snake, telling it: "Go your way... and I'll go mine." Then she opens the door and falls out of the car leaving the snake on the car seat. I was actually relieved that the snake did not viciously attack her, as most snakes do in movies. She'd been through enough trauma already.