Continuity mistake: As the girls run from the killer, the one girl is shirtless as she starts to run, holding her shirt in front of herself to cover her chest. The camera changes to a rear view and now she is running with the shirt in her hand swinging wildly. The camera changes again and suddenly she is running and putting her shirt on, already pulled over her head, a major change from the last shot. Finally, the camera angle changes again and she has her shirt on completely. All of her shirt/hand positions change instantly between shots.
Continuity mistake: When Juan takes his first swing with the axe to break the hot tub, the blade is towards the glass in one shot and in the next shot, the axe is reversed.
Continuity mistake: After Jenny is done speaking with Lars, she picks up a large platter of food and holds it like a waiter/waitress over her right shoulder. (this is a front view) The camera changes to a rear shot and suddenly she is holding the platter over her left shoulder. The scene switches back and she is once again holding it above her right shoulder. This changes back and forth instantly between shots.
Continuity mistake: When Hank and Yu are killed, Hank has the message "Don't let this be Yu" carved into his chest, however, towards the end, when the killer hangs all the dead bodies up in the clubhouse, Hanks shirt is open, and there is no marks on his chest at all.
Continuity mistake: When Lars startles Jenny from behind she lets a mouthful of her red drink spill out, but when she turns around there are no stains on her clothes and her face is perfectly clean.
Continuity mistake: More blood on Kelly's face appears for no reason in the shot just before she's decapitated. (00:06:45)
Continuity mistake: Hank says the killer is left handed but he always holds the knife with his right hand.
Continuity mistake: Juan's shirt is covered in blood before he breaks the hot tub window. Once the water runs over everyone, his shirt is clean. Later, his shirt is covered in blood again.
Continuity mistake: When Lars is first talking to Yu & Stacy, Stacy hands Lars a margerita which is a little more than half full. By the end of the scene, the glass is more than 3/4 full.
Answer: This is a joke referring to the numerous slasher movies where the killer survives all most anything and still comes back. Like when the killer is killed of in the end of the movie but then reappears in the sequel.
Andreas[DK]