They meant that this is fantasy so they (the ones nitpicking on the word futanari like it is an absolute term) should suspend their "normal" beliefs of what is considered normal in a fantasy fictional world.
It is a common expression "suspension of disbelief" and I use it many times when advising someone how to enjoy better sci-fi/fantasy settings or practically almost every fictional genre, that we should enter a suspension of disbelief "state of mind" so we enjoy better those genres, just enjoy the ride, try to not nitpick everything you see because it only give them internal "pain"
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Edit: You can always check this wikipedia entry to better understand the origin of the expression
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I specially enjoy this quote from the wiki entry :
" Not all authors believe that "suspension of disbelief" adequately characterizes the audience's relationship to imaginative works of art. J. R. R. Tolkien challenged this concept in "On Fairy-Stories", choosing instead the paradigm of
secondary belief based on inner consistency of reality: in order for the narrative to work, the reader must believe that what they read is true
within the secondary reality of the fictional world. By focusing on creating an internally consistent fictional world, the author makes secondary belief possible. Tolkien argued that suspension of disbelief is only necessary when the work has failed to create secondary belief, saying that from that point on, the reader ceases to be immersed in the story and so must make a conscious effort to suspend their disbelief or else give up on it entirely. "
Tolkien was really a smart author and an excellent linguist, but in the end is just a question of semantic. I prefer to say suspension of disbelief than "paradigm" or "secondary belief" based on the inner consistency of reality. But I totally agree with Tolkien, sometimes the fictional world is so so so absurd that only by totally suspending disbelief you can enjoy very bad sci-fi/fantasy/fiction
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. What totally isn't the case of Instinct Unleashed, it is not a work of art to the level of Tolkien work but it is a very good narrative for an AVN.