Visible crew/equipment: When Steven carries Jessica to the car, they climb in. Then, as the shot is being filmed very close to the car, a crewmember wearing a white tee-shirt is perfectly reflected in the car window. (01:00:40)
Other mistake: When Robert, who is possessed by Jason, is reaching through the car window to get Jessica and Steven, you can see his reflection on the car hood. This reflection should show Jason, as we've already seen in the movie that the host body Jason is in should show Jason in any reflection. (01:00:50)
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)
Revealing mistake: When Jason (in Robert's body) is shot in the head at the end of the hall, a close up reveals the bullet hole to be obviously just makeup. (01:05:35)
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)
Visible crew/equipment: When Pookie shoots at Robert, who is possessed as Jason, in one side shot you can see Pookie is wearing safety goggles. In all the other shots he has nothing around his eyes. (01:09:00)
Revealing mistake: After Vicki has been killed, Jessica mourns by her body. She then proceeds to stroke Vicki's hair and face. Well, Vicki dies with her eyes wide open. However, as Jessica strokes her face, Vicki closes her eyes. Her eyes then remain closed for all the following shots of her. (01:10:20)
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)
Revealing mistake: After Steven cuts possessed Randy's throat with a machete, you can see that the machete is completely free of blood. (01:15:55)
Continuity mistake: Dirt and grass disappears from the back of steven's sweater, just before Jason throws him. (01:20:10)
Visible crew/equipment: In the finale, Jessica runs over to Jason from behind and she stabs him in the heart with the dagger. Then, Jason lashes back and hits Jessica, and she goes flying backwards. Absolutely anyone can see the large blue crash mat that she lands on (cropped/edited out in some versions). (01:20:25)
Continuity mistake: When Jessica stabs Jason, black blood squirts over his hockey mask, but in the next shot it has gone. (01:20:25)
Continuity mistake: After Jessica stabs Jason he throws her off and she falls backwards, but in the next shot she is turned around and flying face forward. (01:20:25)
Revealing mistake: At the end of the film when Freddy's arm bursts out of the ground and grabs Jason's hockey mask, you can see none of his skin is burnt, like it should be, and also they metal blades on his glove clearly bend like plastic. (01:23:50)
Revealing mistake: If you watch closely, it is painfully obvious that in the beginning, when Jason is getting shot up, they are just repeating the same shot from different angles.
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