My zombie body language analysis...

The "dead" girl appears to display human emotions throughout the film, and takes obvious steps to self-preserve. Some parts of the movie might be confusing, as it can be very difficult to interpret her motives in particular, let alone the other characters. However I believe she was entirely sentient, and viewed in this light a lot of things become clearer. For this interpretation, you have to suppose that perhaps she wasn't a zombie in the traditional sense, in that becoming undead had no effect on her reasoning capabilities, rather she was feral due to mental illness.

When we first find the girl, there are no signs of life. No movement. Then as the guys are wondering if she's even alive and reach to touch her, she takes a DELIBERATE breath. Had she merely given up before, due to lack of stimuli, or was the breathing a conscious attempt at being rescued? She only opens her eyes slightly, perhaps playing unconscious, unless she's just drowsy from a long nap?

Later, JT shows Ricky the twist. She looks dead at first, but then JT is about to shoot and Ricky shouts no, this gets her attention. Not much to analyze there.

Ricky, prone to fainting, wakes up and they are deciding what to do with her, she is looking at Ricky rather innocently, is she giving him the puppy eyes? Then, as JT remarks, "take all the time you need... she isn't going anywhere" she appears to have a helpless expression with tears welling up... though open to interpretation. JT shows Ricky "something"... when he touches the girl, she shakes in fear and braces for an assault, especially when he gets near the genetalia, then when he stops she looks relieved. Watch it and you'll see.

When Ricky returns again, he asks JT if she has been "looking at him, as if she knows something". He corrects JT saying, "she's not just some dead girl"

Then comes the rescue attempt, wherein occurs the most obvious sign of humanity, but also perhaps the most confusing moment in the entire movie for me, but on a fourth or fifth rewatch I finally got it.

He gets at eye level and tells her he's gonna help her. She doesn't respond, not even by looking at him, perhaps in a depressive state? He hears a noise and stands up. After a moment, she SOFTLY touches and practically HOLDS his hand... he gets down again, "Do you understand me? I'm gonna get you out of here, just stay quiet", and then he REMOVES her gag right after telling her to be quiet. He sort of falls apart saying "I'm sorry... I'm sorry" and that is when she looks directly at him.

Then he starts cutting the chains... as the first chain pops, there is a slight movement of her head as she looks up at him. My very open interpretation is that her expression is one of stunned disbelief, and her adrenaline is racing, so to speak. I've come to notice the slightest movement can mean something from this actress in this role.

Here comes the tricky, but not-so-tricky part. He then hears ANOTHER noise, is AGAIN spooked, and STOPS focusing on cutting the chains. THAT is when she grabs his wrist in desperation, as if to say "please just cut the chains and I'll see myself out"... her expression goes from a firm "keep going!!" to one of desperation, and then frustration. When she lets go, she seems to be apologizing? She keeps her hand extended for a long time, and her eyes are widened as though surprised. He then abandons her and she goes back to a helpless expression.

JT mounts her again, at first she tries to act cool, then sees him get suspicious and goes feral, then throws a mini tantrum when tied back up.

The next close-up of the girl is after the boyfriend taunts Ricky about Joanne. She looks right at Ricky with her upper lip drawn. Mirroring the rest of the room, I take this to be her "Oooo damn!" face. She might have known about his crush from conversations in her presence. That's when Ricky suggests "going for the mouth" and she looks at him like "you're an *beep* She rolls her eyes back and does a faint hiss, then another "this is your idea" look. She shuts down and takes it.

Ricky interrupts the 3-way, the boyfriend pushes Ricky, Ricky yells loudly "Stop that $#%!" and the wiener and the girl's face get mutilated in the confusion. Even if there are no tears, anyone can see she is crying a full 2 minutes after the beating.

Another scene has JT putting makeup on her, and she has become docile. When he is threatened by the dog, she kills it and looks to him for approval. Stockholm syndrome? Fear of abandonment? Maybe thought the dog was gonna maul a guy who could make a mistake and give her a chance at escape.

Her reactions during the ending bit aren't very expressive, but they clearly indicate that she is aware of what's happening. They aren't shots of her staring blankly. Then she flips out and kills people.

All of this to me is evidence that she is self-aware and understands her surroundings. Also, she isn't undead, she just can't die, if that makes sense. So calling her a dead girl is inaccurate, and zombie is just plain dehumanizing.