Does no one understand the twist?

I really enjoyed the film and completely understood everything but one scene. In the beginning with the head being thrown out the car window. What was that all about?

I am wayyyyy late to this conversation. I saw this as a case of DID triggered by Marie being conflicted with her feelings for her best friend. During the car ride to Alexia's farm, Marie is having a dream where she is being chased by herself. This is a foreshadowing of the other identity within Marie getting stronger and coming closer to taking her over.

After this the image of the crazy killer trucker appears with a head of a woman with dark hair giving him oral sex. We then see the trucker toss the head out of the window and the head kind of resembles Alexia, white with longish dark hair. That is a second clue that the identity trying to take over Marie has won and has created its own persona and look. It is the corruption of the love Marie feels for Alexia.

I agree Marie is not hallucinating but I disagree with you that Marie is lying. Marie is experiencing the same event as both the killer (her alter) and as the "survivor/savior" (her true self). When Marie fully gave into her lust/desire for Alexia that is when Marie lost dominance and fell victim to her alter, the killer trucker. Marie doesn't know her alter exists or that she is no longer in control.

Throughout most of this we see events through the eyes/perspective of Marie who believes she is saving Alexia. The whole time her alter is in control. Her alter does not know that Marie still has strength and she manages to come out to ask for help when her alter's guard is down.

Marie stayed hidden from the killer not knowing he is her alter, herself. Quite frankly, she never truly knows she is at war with her own self. However, her killer alter does. Remember when the killer asks the gas station clerk what he was looking at (after he kills the clerk of course)? This is the alter realizing, Marie is still active and that she came out and spoke to Jimmy (the clerk).

Marie still is not giving up and is chasing down the her alter/the killer for dominance. The fight between Marie and the killer was the fight for dominance and in the end both identities integrated, but not in a healthy way. Now the integrated Marie is simply a lovesick psycho killer in the end.

Even though the movie did not show this, (and I hope they don't try to make a prequel (or haven't tried it)) I get the feeling the killer is someone from Marie's life, perhaps from her childhood.

Well that is my measly $0.15 on this.

I have no fancy quote or phrase to end this with. 😉

What was the reason for killing the gas station attendant? If Alex is in the back of the truck and the gas station attendant didn't know it, why would she kill him?

Marie is in the car on the drive to the farm house with Alex.
Later on, she goes up to the guest room.
But I think she imagined all that up to the point where she goes outside for a smoke.
When she is outside, that is where her reality comes in. At that point, she is a killer stalking and watching Alex take a shower.
Then she goes back to her truck and masturbates fantasizing about Alex.
Notice that the killer doesn't ring the doorbell until she is done?
Now she is ready to go and kill the family and fulfill her desires for Alex.

I think being friends with Alex and meeting the family was all made up because how else could she have attacked the father at the front door like that and then reached in and unlocked the door?
It would also explain why she had the truck.
And when she goes up to the guest room it is immaculate as if no one had been there but only in her mind someone had been.
How else can it be explained the killer just happens to check the sink which she had just dried?

Damn I'm good.

TY captain obvious

good discussion...

Cecile DeFrance rocks.