Argh. I just watched this. I needed to express somewhere how FRUSTRATED I am at its utter implausibility! I mean, the actual premise isn't that bad. It's just... well... I feel really awful for saying this, but those girls - they were really asking to be made into a centipede. The way they handled things from the very beginning was incredibly stupid.
Spoiler Alert! And warning, for this film contains some nasty themes, as you've probably heard reputed, lol. I don't describe anything in detail though 
If you haven't seen this film, then it can be summed up pretty effectively thusly:
Stereotypically American Girl 1: Let's drive out into the middle of nowhere in an unfamiliar foreign country where we don't know the language, without bringing along a spare tyre or acquiring the knowledge of how to change a tyre, should perchance one of our tyres burst on our creepy creepy journey.
American Girl 2: Isn't that a horror film cliche?
American Girl 1: Yes, but we've got bum-holes surgically attached to mouths later on in the film, so we can get away with a bit of implausibility and everyone will still call this film 'Frighteningly real.'
AG 1: Oh noes! Our front left tyre has burst.
AG 2: Bummer. What should we do? Should we stay with the car? Wait until morning, when there'll be more traffic on the roads and we can flag someone down to help us? Attempt to see how far we can drive with a flat tyre? We might manage to reach a service station.
AG 1: I think we should wander into the woods.
AG 2: Are you sure?
AG 1: Totally.
AG 2: Fine.
[They wander into the woods]
AG 1: OMG! We're lost in the woods!
AG 2: Don't worry. There's a creepy house.
AG 1: Yey!
[They knock on the door. BLATANTLY CREEPY MAN answers]
Blatantly Creepy Man: Hallooooo.
AG 1: Omg, let us in, we're totally lost.
Blatantly Creepy Man: Come into my stark white frightening home. Observe the black candles on the coffee table, and the conjoined-twin foetus artwork on the walls.
AG 2: You have a lovely home.
BCM: Would you like an obviously spiked drink?
AG 1: Yey!
[They chug the obviously spiked drinks]
[Half an hour later]
AG 1: Oh noes! Why am I tied to this hospital bed?!
AG 2: Scream! Let me out! Scream!
Creepy Man: I am going to sew your bum holes to each others mouths and make you into a human centipedy thingy along with this young rather attractive East Asian man.
AG 1: Oh noes!
Creepy man: First I am going to leave you alone for a couple of hours while I do weird creepy things.
[A couple of hours later]
Creepy Man: Now it is time for the loony operation! Don't worry - I did this with some dogs first.
I will inject you all with general anaesthetic! Yey.
First the East Asian man.
Then American Girl 1.
Ho hum. Ho hum hum.
AG 2: Oh. These arm restraints come right off if I actually try.
I am escaped!
[Run run run]
Aha! An open window! Should I run to freedom and get help?
No. Best go back down into the cellar-cum-operating room, untie my irretrievably comatose friend and attempt to drag her unconscious dead weight out with me at a snail's pace.
Creepy Man: Aha! I have caught yous.
AG 2: Oh noes!
[Centipede operation]
Creepy Man: You are now a centipede! Do things!
Centipede: No. You're mean.
[Days pass. Two policeman come knocking on the door of the Creepy House]
Policeman: We suspect you've kidnapped some peoples and made them into a centipede.
Creepy Man: Who, me?
Policeman: Yeah.
Creepy Man: Would you like an obviously spiked drink?
Policeman 2: Yey!
[He chugs the obviously spiked drink]
Policeman 1: Now we've partaken of refreshments, we'll be back in fifteen minutes with a search warrant.
[Meanwhile, the centipede has managed to get hold of a scalpel]
Creepy Man: Hello, Centipede, how are you... ARGH! You've stabbed me in the leg! Argh! You've bitten me once in the neck! I am all collapsed. You should probably check that I'm actually dead, though, before you g... oh well. He's gone.
Policeman 1: We're back!
Policeman 2: I don't feel so good.
Creepy Man: I'm still alive! I shall overpower and shoot Policeman 2!
[Gunshot]
Policeman 1: Oh, my colleague is shot! I'll just stand here and wail my colleague's name as I look at his dead body in the water of this swimming pool, without looking around at all to see whether his assailant is still in the r... oh poo, I've been shot too.
[Elsewhere in the house]
Man at front of centipede: I succumb to horrendously stereotypical Japanese self-flagellation! I am an insect! I deserve all of this. I kill myself.
Girl at back of centipede: I have ingested too much recycled poo. I die.
Girl in middle of centipede: Oh crap.
[Trees].
'Vote for E.L. Wisty, or invisible nudists will come along and smash you round the face.'
(E.L. Wisty)
