Let's assume that at least some animals are capable of thinking despite lacking a language. This doesn't necessarily mean that they possess concepts, for some forms of thought may be nonconceptual. We can imagine, for instance, a squirrel who is planning how to get from the branch she's currently standing on to a branch from the tree in front. To do this, in principle she doesn't need a concept of branch nor a concept of tree. It might be enough for her to have, for example, the ability to think in images; to make a mental map of the tree where she can imagine and try out different routes. This doesn't imply that squirrels lack concepts, simply that they don't need them for this concrete form of thinking. For us to be able to say that an animal has concepts, we have to show not just that she's capable of thinking, but also that she has certain specific abilities.