I know how to run your code.

Its right there in the code

It doesn't follow the specification: you haven't implemented a static method.

I didn't implement a static method because its just extra indirection -- the spec contains enough indirection on its own, it doesn't benefit from extra confusion

Speaking of which, you say it should return

 ( [],
  [ 'Dog', 'Wolf' ]
)
[download]

That is kind of a surprise compared to your original sample data and sample ooutput ... as it stands my "solution" isn't there yet