In her InSIS seminar as part of the STS Issues in Scale series, Gail Davies (University College London) described some of the many ways in which the genetically engineered mouse, central to so much of today’s biomedical research, helps us rethink the scalar relations of scientific productivity. The ‘humanised mouse’ is a widespread instrument of knowledge production and clinical translation in contemporary medicine: by redesigning the genome of laboratory mice, researchers can mimic in the lab certain aspects of human biology and experiment in vivo without the risks and hazards of involving human subjects.