Continuity mistake: Frederick picks up a bottle of champagne out of the ice bucket and shakes it a little. As he does this the foil and wire are still on top. He turns and aims the bottle at his wife, then tips it back and the foil has vanished as he now just removes the wire and cork.
Continuity mistake: When Annabelle gives Frederick her gun, he places it in the mini-coffin and closes the coffin. However, in one of the next shots, we see that all coffins are open.
Suggested correction: It's not "in one of the next shots" it's actually many shots later, so anyone could have touched that mini coffin for any reason during the time off-screen. After Frederick closes the top of the mini coffin, it cuts to the scene upstairs with Nora and the missing severed head. Then a considerable period of time has passed until we see the mini coffins again, when Lance walks into that room and sees Pritchard with the knife.