Continuity mistake: When Phil, who is possessed by Jason, has Josh tried up inside the Voorhees house, he takes some shaving cream and puts it all over Josh's moustache. However in the next shot there is suddenly much more cream on Josh's moustache/chin. (00:35:45)
Continuity mistake: After Jessica shoots Josh in the head, he lies on the floor and his tee-shirt is clearly untucked. But when he grabs Jessica, and then wrestle on the floor, his shirt is now tucked in. (00:38:00)
Continuity mistake: When Josh is attacking Steven, after Steven tried to save Diana from Josh, the small table with a lamp, photo frames and other ornaments on it has half it's items knocked off, with a couple of ornaments remaining on it. In the next shot, these ornaments have also gone. In addition, the green rocking chair next to the table, has a decorative cloth sitting on the seat of the chair, but in the next shot the cloth is draped over the back of the rocking chair. (00:38:45)
Continuity mistake: When Jason is attacking Steven in Diana's house, before Steve impales Josh (who is possessed by Jason) with the the poker, Josh lifts his head to look into the mirror but the reflection of Jason stays still. (00:39:15)
Continuity mistake: When Steven impales Josh with the fireplace poker, Josh starts to stumble very slowly toward the window, but in the next shot, he is moving with enough force to move across the room and shatter through a window. (00:39:25)
Continuity mistake: When Josh is impaled by the poker, he stumbles towards the window and crashes out of it, pulling the white curtains with him so that they drape outside the window. But in the next shot the curtains are pulled back neatly inside the room once again. (00:39:30)
Continuity mistake: When Josh attacks Diana, Steven tries to save her. We see Steven being taken by the police and his blue jeans are spotless. Yet in the very next scene of Steven talking with Randy at the station, Steven's jeans are now soaked in blood, for no apparent reason. (00:40:35)
Continuity mistake: When Vicki is cleaning the bloodstain from the carpet, Jessica enters the room and they talk. Between shots the yellow rubber gloves and the small sponges which sit on the bloodstained carpet change position. (00:41:30)
Continuity mistake: In the police station, Jessica gives a rubber duck to Stephanie in one shot, but in the next shot it has gone. It returns in the following shot. (00:43:55)
Continuity mistake: When Josh transfers the Voorhees creature into Robert's mouth, blood runs down Robert's right cheek as this transfer is made. Once Robert then wakes up as Jason, the bloodline has swapped cheeks. (00:56:40 - 00:58:00)
Continuity mistake: When Steven runs possessed Robert over, black blood covers all of the bottom of his shirt, and all his trousers. But later, when he comes to the police station they're clean. (01:01:10 - 01:06:00)
Continuity mistake: When Steven is fighting with Randy by the police car, you can clearly see in one shot that he has his gun in the back of his pants, but later he pulls the gun out of the front of his jeans. (01:03:15)
Continuity mistake: When Randy drives out to pick up Steven, Randy takes off his police hat and puts it on the hood of the car. Randy then punches Steven, and in the next shot you can see the police cap has vanished from the hood. Cut back and it's there again. (01:03:15)
Continuity mistake: When Steven gets punched by Randy there is blood filling his mouth, but a few seconds later there is barely any blood on his lips. (01:03:25)
Continuity mistake: When Steven jumps upwards, and out of his handcuffs, he knocks out the policeman who was walking with him. As the policeman falls to the floor, his hat falls off. However in the next shot the unconscious policeman is lying on the floor with his hat back on his head. (01:05:20)
Continuity mistake: The note that Jessica found in Stephanie's crib changes. When she finds it, it reads "I have what you want " and is written in blue ballpoint pen. But when Steven finds the note later, it reads "I have your baby " and is now written in thick, black permanent marker. (01:08:35 - 01:11:15)
Continuity mistake: When Jessica arrives at the Voorhees house, her neck is clean, but when she enters the room with Duke in it, she has a black handprint on the side of her neck. (01:11:30)
Continuity mistake: The blood vanishes from the pole which goes through Duke's leg. (01:14:55)
Continuity mistake: Dirt and grass disappears from the back of steven's sweater, just before Jason throws him. (01:20:10)
Continuity mistake: When Jessica stabs Jason, black blood squirts over his hockey mask, but in the next shot it has gone. (01:20:25)
Answer: There isn't much of a feasible in-movie explanation. In truth, the entire scene was added by the director because he felt the movies were pretty sexist in that it was mostly women who were either nude or sexualized. Thus, he added an inherently homo-erotic sequence involving one man shaving another stripped man to "level the playing field" so-to-speak. The only real explanation I could think of is that maybe the creature just thought it'd feel uncomfortable transferring to a man with a mustache. But even that's shaky at best.
TedStixon