Continuity mistake: When Agent Marcus arrives at the Crystal Lake cabin at the start, the sun is low, but the sky is still bright. In the next shot as she goes into the house, the sky is pitch black. (00:01:10)
Continuity mistake: When the light bulb explodes, Agent Marcus takes the old, burnt bulb away, and puts it on top of the metal ladder she's standing on. In the next shot she descends the ladder and folds it up, with the old, burnt light bulb having mysteriously disappeared. (00:02:50)
Continuity mistake: When Agent Marcus is replacing the burnt bulb while standing on the ladder, between shots the bill of her baseball cap folds itself upward. (00:03:00)
Continuity mistake: The white sweater, tee-shirt etc., that Agent Marcus throws in a heap beside the sink change position from when she runs the bath, to when the lights go out. (00:03:45)
Continuity mistake: There are two times after the female FBI agent gets out of the shower that she is wearing underwear when she put none on, and the pair that she has on is completely different from the one she originally took off. The first is when she runs directly to the door from the shower after the power goes out. The second is seen when she puts on only a towel shortly after, and then falls over the railing, you can see she's wearing underwear there as well. (00:04:45)
Continuity mistake: After the female FBI agent falls over the railing and through the coffee table, the two legs closest to the screen roll away, but when the table is shown again, the legs are underneath it. (00:04:50)
Continuity mistake: At the start of the film Jason chases Agent Marcus from the cabin, and she is barefoot. But in the shots of her running through the woods, in some shots she is barefoot, in others she has white socks and big black boots on, and in others she has flesh-coloured trainers on. (00:05:10)
Continuity mistake: On the field where Jason is being shot, Jason is equipped with a machete in his right hand. However when they drop the bomb onto him, Jason hears it and looks up, and in this shot you can see that Jason's machete has disappeared. (00:06:35)
Continuity mistake: When the coroner sees Jason's heart beating, from shot to shot he has a little blood, then a lot, and then just a little again, but when he goes to actually eat the heart there is a lot of blood smeared on his cheek and face. (00:12:30)
Continuity mistake: When the coroner is inspecting Jason's body he is wearing a watch on his left wrist. While he is eating the heart the watch disappears but returns after he is possessed. (00:13:35)
Continuity mistake: While eating Jason's heart, the coroner's shirt is covered with the fountain of black fluid coming from his mouth, but when the assistant coroner comes in there is far less liquid on his shirt. (00:14:00 - 00:16:00)
Continuity mistake: When the Coroner is stopped by the two security guards, he places his pizza box a bag of drinks down on the table. One guard then pats him down and then in the next shot the position of the drinks bag on top of the pizza box has changed. (00:14:40)
Continuity mistake: At the diner where the Jason Burgers are being sold, Ward complains about not being able to make the patties correctly, so Joey demonstrates. As she makes the two eyeholes with her finger, the patty changes places on the counter between shots. (00:20:20)
Continuity mistake: In one inside shot of the tent, Luke is lying down on his chest and he turns the lantern on. In the very next shot from outside, it shows his shadow cast from the inside of the tent, and he is now sitting up. (00:26:30)
Continuity mistake: When Alexis is outside by the campfire, she is fiddling about with a blue sleeping bag, which is rolled up in a bundled circle. However in the next shot the sleeping bag is suddenly rolled out flat across the ground, and Alexis now unzips it. (00:26:55)
Continuity mistake: When Deborah returns back to the tent, it pans across to show the dead body of Alexis propped up against a tree. In a following shot from the point of view of Phil, who is possessed by Jason, watching the tent from beind some leaves, you can see they body of Alexis has now gone. (00:29:55)
Continuity mistake: The pole that impales Deborah moves from going though her chest just below her boobs, to much lower down, in her waist between shots. (00:31:55)
Continuity mistake: When Deborah is impaled with a post in the tent, the amount of blood on Luke's face decreases between shots. (00:32:00)
Continuity mistake: When Diana walks out of the doors carrying a silver tray, you can see inside the tray and it is completely empty. However in the following shots as she walks across the car park, there is now a white bowl of dog food inside the previously empty tray. (00:32:20)
Continuity mistake: The position of Edna's headscarf changes between shots before her head is slammed in the car door. (00:34:55)
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