Other mistake: When Amy and Evil are at Peter Vincent's house to convince him to help Charlie, you see them looking into a horizontal mirror that's on the wall on the left side of the screen. If you actually look at the reflection, Evil is on Amy's right. However, he's on her left in reality.
Continuity mistake: When Evil is below the staircase transforming from wolf into man, he grabs hold of the table leg lodged in his chest. Between shots he goes from using one hand, then two. (01:21:50)
Continuity mistake: Right before Jerry busts through a stained glass window, Peter can be seen holding a wooden table leg - which was driven through Evil's wolf form earlier. In the following shot the leg is nowhere to be seen. (01:32:00)
Continuity mistake: After Amy punches Evil and shoves him aside, he grabs hold of his right arm. Between shots, he lets go of his arm. (00:41:35)
Revealing mistake: As Jerry leaves Mrs. Brewster's bedroom, a mirror reflection shows the door opening a crack before he even touches the knob. (00:27:00)
Revealing mistake: During the basement finale, lines can be seen suspending Jerry in the air when he lunges towards Peter and sends him crashing into some shelves stacked with glass bottles. (01:37:55)
Revealing mistake: When Jerry is dragging Charley across the bedroom by his neck, he turns around and slams him into a wall. It wouldn't be unreasonable to assume that once his head makes contact, the wall's gonna break somewhere. But notice how the wall is already cracked right above the classic convertible picture a split second before it should be (widescreen only). (00:29:05)
Answer: Peter's odd behavior at Jerry's house made Jerry suspicious. When he discovers the shard of the mirror on the ground he finds out why Peter was spooked: Jerry doesn't cast a reflection. Jerry then decided that Charley's friends must be dealt with. In Ed, Jerry sees something which would lead him to believe Ed would make a good servant. Jerry turns Ed into a vampire and sets him against Peter while he himself deals with Charley and Amy.
BaconIsMyBFF