Probing the emotional lives of animals is new territory for biologists. A couple of decades ago, emotions were off-limits: scientists studying animal behaviour focused on what they could see animals doing, not how they might be feeling. Yet questions of animal emotion underpin animal welfare – as Jeremy Bentham wrote in 1789, “The question is not, ‘can they reason?’ nor ‘can they talk?’ but ‘can they suffer?’” The growing animal rights movement forced us to consider animal emotion, and we now know a great deal about how the vertebrate brain generates and makes use of what we humans experience as “feelings”.A whole other layer of complexity arises when thinking about the animals that share our homes, especially dogs. Most dog owners are convinced that their pets not only lead complex emotional lives, but also know what their owners are thinking. Study after study seems to provide support for these notions: most recently, scientists at the Messerli Institute in Vienna have shown that dogs can discriminate between human faces that are expressing different emotions, even when they can only see half the face, and the person in the photo is completely unfamiliar to them.