When we think of animals, we focus on mammals and birds, but 99% of the animals on the planet are invertebrates. We dismiss them as simple, with automatic behaviour and limited senses--not true. So, before we learn their abilities and try to figure out if invertebrates are sentient, we have to define what sentience is. Is it having intelligence, using it to understand the environment, solve problems and predict the future? Is it using self-monitoring, having a sense of who you are, and also having feelings, a subjective approach that puts value on things. But we will never really know what another species is actually feeling inside. So, for invertebrates, it is tough. We do know some things about some of the invertebrates. Octopuses gather information, attend to important stimuli, and plan for the future. Hermit crabs place value on shells used as shelter and fight harder for desirable ones, they feel and avoid pain to stimuli that we find painful, and octopuses do too. Bees pass information along in a colony by watching others, observational learning. Probably some invertebrates have some sentience, though maybe not the same kind as we mammals have. Why should it matter? If we think animals can anticipate situations, plan for the future have values, we shouldn’t treat them as just ‘things’. We should treat them with care after we find out what that means. And yet…. shouldn’t we treat all animals well, even if we don’t believe that they plan, think and feel?