Continuity mistake: After Jimmy draws the pentagram on his hand to connect the dots, he holds up his hand to show his sister and the drawing is different from the one shown before. The outline is much darker.
Revealing mistake: When Christina Ricci picks up the silver knife off the floor in her house and her hand starts to smoke, pay attention to the shadow. You can see smoke coming from her wrist before her hand touches the knife.
Continuity mistake: When Christina is talking with the blonde girl in the office (after the first werewolf attack) the blonde's hair is down on one side and tied on the other. Right after the last shot of Christina, suddenly her tied up hair is down and flawless.
Continuity mistake: When Bo goes to kiss Jimmy after telling him that he is gay, the facial shot of him shows his head moving to kiss Jimmy by turning to his right. But in the shot when we see behind Bo his head is turned to his left.
Continuity mistake: When Zipper takes the steak off the counter, its obviously raw, but when he has it in his mouth and walks away with it, its completely stiff as if it's frozen.
Continuity mistake: When Jonie is killed as werewolf, she lands on her back. When the police officers come to look at her, she's on her side.
Chosen answer: Joanine made a crack saying "I guess there is no real way to have safe sex with a werewolf. Joanine dated Jake before Ellie, hence how she became a werewolf before Ellie and Jimmy. In fact it was Joanie who made Ellie and Jimmy werewolves because she stated she was killing the other girls Jake was interested in.