There's always been a little disturbance in the force known as cryptozoology, one that gives the field some of its difficulties in achieving scientific credibility. Some zoologists look askance at the whole endeavour because of the perceived focus on animals such as sasquatch which are perceived as highly unlikely, if not absurd. I have no problems here: as long as the chance of finding an animal is not zero, people can look without making the field scientifically invalid. In science, most long shots don't pay off, but some do. The key is whether searching is being done in a scientific manner, proceeding from the evidence to gather more evidence and meeting Popper's classic criteria of the falsifiable hypothesis. (There can be disagreement on how much negative evidence, or how strong a logical case, is needed to falsify a given hypothesis, but the point is that a hypothesis like "There is a large unknown primate in North America" is perfectly scientific. The means to search every possible chunk of forest habitat definitively are not available, but the reasoning is fine.)
Then we get into another problem: the allegedly paranormal/psychic/parapsychological nature proposed for some cases. I don't mean to pick on Nick Redfern, a very dedicated researcher, and a most enjoyable and often thought-provoking writer, but having just read his book Monster Diary, he is the example that comes to mind when thinking of people who class things that look like animals under cryptozoology, even if they are clearly not physical animals. I'm well aware that sane and sober people have reported apparitions, and I have no particular insight into what mix of causes is behind that phenomenon. It's not my field. But here's the part where I and Nick depart ways. He and other other like-thinking investigators argue that apparitions of animals are part of cryptozoolgy, and, as Nick puts it in his book, cryptozoologists in some cases will go on chasing sightings without results "unless the field of cryptozoology wakes up and and realizes that there needs to be a new approach to the subject."
I would flip that around. My position is that, if there is no physical animal, or no reasonable chance of one, the case no longer pertains to cryptozoology or any kind of zoology. If someone believes they saw a sabretooth tiger that disappeared into thin air, for example (and this happened, as Nick recounts) , then the fact that the apparition was in the form of an animal doesn't put the event under the heading of cryptozoology. It can be parapsychology or any other field one may think appropriate, but if it's not zoology, it's not cryptozoology. People who thing sasquatch is so elusive because it's not a material creature are welcome to hold that opinion, but they shouldn't call that topic part of cryptozoology. It's part of the whole business of apparitions and spirits and the paranormal. It also, critically, is not a falsifiable hypothesis (you can never prove such a belief to be wrong) and therefore is not part of the physical sciences. If a definitive search (in the cases where it's possible) fails to find an animal, then it's because the animal either did not exist in the area, has gone extinct, or has migrated elsewhere.
An animal is by definition a physical thing of flesh and blood. It's there or it's not. I don't dismiss the possibility of a nonmaterial reality: as a Christian, I believe strongly that the material universe is not all that exists. But an apparition is not an animal, any more than it can be a human being. It may be reported sincerely to look like one, or even act or sound like one, but that's not the same thing.
I wrote in my 2006 book Shadows of Existence that I was dismayed that a very good book by Healy and Cropper on Australian mystery animals spent a chapter on "zooform phenomena" after spending the rest of the book scientifically discussing unknown creatures. I feared that zoologists would dismiss the whole book because of this direction. I don't know how to take a survey on this, but I have no doubt I was right, and still am. Cryptozoology will never get the respect of zoology if paranormal entities are part of it.
And, if cryptozoology is the search for hidden ANIMALS, then they should not be. The experiences of people who see a big cat seemingly dive into the ground and vanish, or a small herd of camels appearing where none can be, are not beneath our notice. They are simply part of another field of study.