The Puzzle of Similarity is a problem for animal experimentation in general but it is especially troublesome for models of pain. It can be stated as follows: If animal models (of pain) are valid, they are morally impermissible and if they are morally permissible, they are useless. Either way, experiments involving animal models (of pain) should be abolished. The puzzle arises from the clash of two normative prescriptions imposed on animal experimentation by epistemology and ethics. Epistemology prescribes increasing similarity between humans and animal models. However, too much similarity may entitle animals to protection against harmful experimentation. The purpose of this paper is to solve the puzzle by reconciling the two normative prescriptions, at least for some animal species. The position defended is that at least some animal models of pain could be validated as representations of human experience of pain without featuring animals that experience pain.