For most people, being conscious is proved by things like mourning dead companions, like caring for your babies and showing distress if they are missing/hurt, like being friendly and playful. That's why most people feel that certain animals they interact with more or have seen on TV are conscious (dogs, cats, elephants, whales, chimps and other primates), but that other animals are not (insects, rats, fish). Note that I am not saying that rats are objectively less conscious than dogs by these criteria, just that this is what many people base their beliefs on, and that it of course depends on their knowledge as well.