While not all animals share the same biological or seeming phenomenological components--for an example of the former, sea sponges do not reportedly have any neurons [1], unlike humans, and for an example of the latter, sharks have electroreception, unlike humans--all biological creatures are animals. This includes people. We have stomachs and excretory systems like dogs and bears, we have eyes and hands as do chimpanzees (which are supposed to share almost 99% of the same genes with us) and gorillas (with which share slightly less generic overlap), and we consume food and water to survive as do lions and ants. None of these examples of similarities are necessary to realize that humans are animals because any bodily creature would have to be one.
Some people are fiercely offended by the fact that being different from other animals does not mean we are not animals ourselves. Not that dissatisfaction or dislike would make it true or false, the concept they might hold to instead denies the massive overlap between humans and the creatures of the land, air, or sea. We are heterotrophic (we eat other organisms for food rather than producing our own through photosynthesis like plants or chemosynthesis like some deep ocean life), we reproduce sexually as most animals do, and we have organs like lungs and a heart that can also be found in many other creatures. We eat, drink, and can die as they do. We pass on and inherit genes. We can succumb to sickness.
The exact physical differences between humans and other animals depend on which animal is in question, for some are far more like us in form than others. Humans have nonetheless outwardly dominated the planet by civilization and technology, though the natural world can still easily render us incredibly vulnerable, and though it is really the capacity for intelligence, despite many people never becoming rationalists and thus never truly being rational, that has enabled the doability of these things. Of course I still cannot know just how phenomenologically similar other animals are to me as opposed to how similar they seem, for not even the minds of other humans can be known by a non-telepathic/omniscient being to exist or to be experiencing specific things at a given time!
It is at its core mostly on the basis of religious or other spiritualistic metaphysical philosophies that some people think humans are not animals instead of being unique animals, although there is nothing logically contradictory about being an animal and, say, having an afterlife of some kind or being created or guided by God for a higher purpose; none of this contradicts logical axioms, so it is possible and thus could have been true even if certain aspects are not. It also possible that other animals either do or do not have afterlives but not humans, for humans to have or not have afterlives but not other creatures, or for all, some, or no individuals from each species to have one. There is nothing about being human that has to entail this sort of nature to the exclusion of other animals sharing the same.
We are mental beings with physical bodies. Our bodies, as far as scientific evidence from microscope observation suggests, are themselves made of cells that in turn contain genetic material, as is the case with animals. Humans do not have to be as distinct as possible from other animals to be different from them, but, again, being different does not necessitate that humans are not animals. As established already, people could only be animals. It in part, besides misconceptions about the logical consistency between spirituality, certain specific religions, and this fact, a passive neglect of looking past words to ideas could make this idea unpopular. Words cannot force anyone to believe in fallacies and errors. Even so, common references to other creatures as animals without using the same word for people could lead to assumptions by some that humans must not be animals. It all would depend on what is intended by the words as to whether someone errs by referring to people and animals using different collective terms.