I was talking with a playwright friend the other day about a review he had received. He made the point that at times, while a specific criticism may not itself be valid, it may be a symptom of a problem area, a sign that something needs fixing, even if its not the something the critic thinks. These kinds of criticisms are the mutant frogs, those signals that all is not right in the waters or ecosystem of your written work. I had a similar experience in getting critiques of my novel and the mutant frog comments helped me identify the areas of the book that had not kept pace with the continuing evolution of the characters, often sections that were holdovers from an early draft and no longer fit the direction of the story.
I like this notion of mutant frogs as a way of hearing criticism. Look past the surface of the critique. Does it point you toward an area of toxic waste in your work?
What signs serve as your mutant frogs, clues that something is amiss in your work? What about canaries in the coal mine (not to batter my metaphors too badly)? What signals tell you when to cut your losses on a piece as being too toxic to support life?