In special cases of partial twinning, two heads, each supporting a more-orless
normal human mental life, emerge from a single torso. It is often argued that there
must be two people in such a case, even if there is only one biological organism. That
would pose a problem for ‘animalism’, the view that people are organisms. The paper
argues that it is very hard to say what sort of non-organisms the people in such cases
would be. Reflection on partial twinning is no more comfortable for those who think
we’re not organisms than for those who think we are. We may have to accept that a
single person could have two separate mental lives.