Consider this review audit. The post appears of good quality, but the expected action is not to let it through (i.e. downvote, flag or edit).
The reason is that the post is actually a copy of an existing answer. Note that comments are not visible during the audit.
I happened to pass this audit only by accident, because I wanted to edit the post to add backticks to code pieces. But the risk is high that the next reviewer upvotes this (or a similar) post and fails the audit.
I've suggested to show other answers next to the target post during review, which would help in this case. But it would make reviewing a much more time-consuming task.
Flag as "Plagiarism"?
Another option is to add a separate reason for flagging:
I am flagging this answer because ...
... it is a copy of an existing answer (~> "Select original answer" dialog box)
and to exclude the answers flagged this way from review audits.
There's the problem, however, that several persons could be writing answers at the same time and posting them in short time intervals. It is very common that a trivial question like
How do I print to console in Java?
receives many almost identical answers:
You do this like
System.out.print();Hope it helps.
For such cases, I'd suggest that only late posts would be allowed to be flagged as clones. Besides, heuristics could be used for the final decision (whether the flag passes through to moderators or not), like length of the original post, reference to the original post inside the clone, amount of code copied from the question, etc.