2 large mistakes (spoilers)

Ive come across 2 quite large mistakes in the movie, at least I think they are and was wondering if anyone had any suggestions on them.

1) The killer cuts off his nipples in the beginning if I recall. Throughout the film we see the culprit topless and his nipples are perfectly intact and later the nipples are found in the accountants drawer, I assume they were planted there by the killer but if the killer didnt cut off his nipples as evidenced by the fact he still has his nipples in later scenes when hes topless does that mean that the accountant was the one making the phone call and cutting off his nipples despite not being actually Bobo the clown.

2) Bobo is in a phone booth talking to Camille. When asked for her name Camille thinks for a second and says "Karen". Later we cut back to the phone booth to reveal Bobo has replaced himself with a pre recording of his voice and as she listens to him he sneaks in her house and kills her. Nothing wrong with that, except that on the recording he says hes upset she lied to him when she called herself Karen as he knows thats not her name. Now unless Bobo is psychic how did he know she was going to give Karen as a name. Yes his girfriend works there and she couldve filled him in on the police trap but it really seemed like she pulled the name Karen out of thin air so how did he know exactly that she would say that to him so he could make a recorded response and play that to keep her on the phone.