Audio problem: When Chatterer appears and shoves Frank back in the attic, we get a closeup of his teeth chattering, but when it cuts to a wideshot, he's no longer doing it. You could argue that he just stopped as the camera cut (a little flimsy, but arguably a valid correction), but the real issue? They continue to play the "chattering" sound effect for about a second after he stops even though his teeth are no longer moving. They try to mask it by fading it out quickly... but it makes the moment feel wonky.
Audio problem: When Steve and the nurse discover Kirsty has fled the hospital, their lines don't quite match their lip movements when they are on-screen. Especially when Steve says "Maybe she's gone back to..." (Several characters were redubbed with American accents in post, which may explain the discrepancy). (01:10:04)
Audio problem: When Julia and Frank are talking after Kirsty first encounters the cenobites, if you look closely, Frank's words don't quite match his lip movements a few times. It's especially noticeable when he snaps out "What I care about is a new skin!," which doesn't match in the slightest. (01:09:15)
Audio problem: When Steve says "What?" to Kirsty at the pet-store, it's pretty painfully obvious that the line was dubbed in during post. The audio is much more loudly spoken than he appears to be speaking. (Several characters were redubbed with American accents in post. Presumably this is the reason for the inconsistency). (00:45:33)
Audio problem: When the cranky lady at the pet-store demands "Where's the manager?!," the audio and her lips don't quite match.
Audio problem: When the moving man says "That your daughter?" to Larry, the audio doesn't match the lip movements in the slightest, revealing the line was dubbed. (Several characters were redubbed with American accents in post. Presumably this is the reason for the inconsistency).
Audio problem: When Kirsty first encounters Frank, he says "It's Frank! It's uncle Frank!" When he says "uncle Frank," the audio and his lip-movements don't quite match.
Audio problem: When Kirsty is flirty with Steve at dinner and he says "So lay down," the audio doesn't QUITE match his lip movements. (Several characters were redubbed with American accents in post. Presumably this is the reason for the inconsistency).
Audio problem: When Kirsty enters the house and the moving man says "My lucky day!" his words don't quite match the lip movements, making it obvious the line was dubbed in post.
Audio problem: When the unnamed Asian man sells Frank the box at the beginning, watch when he says the line "it always was." The words don't quite match the lip movements, revealing the line was looped in post.
Answer: Letting the moviegoers know what happened to him, he was no longer human, but a piece of meat to be butchered.