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Are birds mammals? The answer to whether birds are mammals has long been debated, and there are many reasons why some people think that they aren’t. First of all, mammals are vertebrates, but birds are not because they have hollow bones and feathers instead of fur. Birds also lay eggs, …

If you’ve ever owned a fish tank, you’ve likely noticed that your fish swim back and forth endlessly during the day. This seems to support the common belief that fish sleep in the same way humans do, by shutting down one hemisphere of their brain at a time as they …