A recent issue of Interface Focus examined the idea of convergent minds, which pertains to how distantly related species can think about problem solving in very similar ways. The special issue is a multi-disciplinary investigation into the evolution of cognition and its various forms. One of the papers, a research article called ‘Representation of different exact numbers of prey by a spider-eating predator’ shows that spiders can differentiate between one, two and many. We spoke to authors Fiona Cross and Robert Jackson to find out more.