This paper constitutes a speculative bioethical intervention into the challenge of developing cultures of care and assembling enriched environments for genetically-altered mice in laboratory environments. The principles of the 3Rs-to reduce, replace and refine the use of laboratory animals-established in the late 1950s, are still the institutional and international starting point for humane animal experimentation. However, the proliferating diversity and numbers of genetically-altered animals used in biomedical research is a challenge to the application of these universal principles. The different capacities of the many mice brought into being through scientific practices constitute biomedical experimentation as a multiple, challenging the identification of universal refinements. In this paper, I argue they constitute a multitude: their indefinite number and irreducible multiplicity is both a threat to these principles and an opening to the possibility of new bioethical formulations. Drawing on ethnographic research with scientists and policymakers involved in animal welfare and biomedical research, this paper explores emerging strategies for reassembling animal welfare in the face of the multitude and the multiple. Using insights from Žižek, Haraway andHinchliffe it seeks to demonstrate the value of a speculative ethics, which, instead of the seeking new universal principles to protect animals from harm, starts from the inevitable and particular entanglements of animal and human suffering, as a way of connecting affective capacities across space and time. This is illustrated through the experimental conjunctures of barbering mice. In conclusion, I suggest such speculative bioethical formulations may contribute to renarrating modes of ethical engagement when sociotechnical assemblages are complex, objects and ontological forms are multiple and mutable, data is simultaneously abundant and inadequate, and formal ethical review procedures are incapable of either containing controversy or enabling critique. Birdsong: A CD of various songbird songs downloaded from the internet, played back through a personal CD player and two miniature earphones Shadows: A 15 cm diameter white cardboard disc with leaf shaped holes covered in yellow, blue, pink and white tissue paper, rotating at one revolution/minute This strange catalogue of artefacts goes on for over two pages of the appendix of an academic paper (Nicol et al, 2008) 1 . There are more than twenty objects and other entities listed, gathered into three broad categories: i) edible/large/replaced, ii) shelter/hard/outside, iii) soft/replaced/chewable. It is a compelling and demanding read. In this quixotic mix, the objects have an apparently tenuous connection to each other, but are enumerated with remarkable precision and specificity. The list is reminiscent of the impossible taxonomy of Borges, which opens the preface to The Order of Things (Foucault, 1970). There is the same incongruous juxtaposition found in the categorisation attributed to a certain Chin...