Other mistake: Before the wolf changes back into Evil Ed you can see the black cables pulling the fake wolf across the carpet.
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.
Other mistake: When Jerry is in the nightclub starring at Amy you can see his reflection in one of the mirror columns of the dance floor. He is a vampire and shouldn't have a reflection. (01:02:51)
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