No idea where you "looked it up", becuase that's hardly a valid definition. Modern taxonomy is rather complicated and is not particularly concerned with kingdom

No idea where you "looked it up", becuase that's hardly a valid definition. Modern taxonomy is rather complicated and is not particularly concerned with kingdoms (like Animalia), which are used more because they are handy to use, not because there is a real strict boundary between what is an animal and what isn't. So they have rather loose definitions. Your statement lacks definition of what exactly is a "stomach", and I don't think you can provide such a definition for it to classify animals correctly. Sponges (which are animals), for instance, don't really have a "stomach", there is no cellular differentiation based on that function. Many carnivorous plants (which are not animals based on that they are plants, a different kingdom), on the other hand, do consume other living creatures and have something that can be considered "a stomach".