Are you a man or a mouse? This expression is used to encourage someone to be brave when they are frightened of doing something. It is also an expression which bears associations to John Steinbeck's novella Of Mice and Men, the title of which is taken from Robert Burns' poem To a Mouse, which is often quoted as the best-laid plans of mice and men often go awry. Thus, the title's ambiguity sketches not only the issue at stake in the current debate on the creation of chimera, hybrids and cybrids (cytoplasmic hybrids) for research, but also provocatively encourages us to regard this new possibility as an important step towards fulfilling the golden promises of stem cell research while simultaneously summarizing the worry that the creation of interspecies organisms is a slippery slope towards ‘the apocalyptic end of humanity'. The proposal to conduct cytoplasmic hybrid research raised by British researchers in applications to the British regulator, HFEA (the Human Fertilisation and Embryology Authority) sparked worldwide debate and controversy reflecting a fear that this type of research was a slippery slope towards creating actual beings that were part human and part animal. The scientific community was, however, successful in explaining to both the public and policy-makers that this new technique did in fact not entail the creation of actual live interspecies beings, but rather provided a way forward in studying diseases in the petri dish and thereby improving chances of offering new therapeutic applications in the clinic.This new scenario poses several challenges to traditional legal categorisations, which this paper intends to highlight.