  Terms are suggested for inclusion in a Lagrangian density as seen by an
observer O2, to represent the dynamics of a quantum mechanical observer O1 that
is an initial stage in an observation process. This paper extends an earlier
paper which suggested that the centre-of-mass kinetic energy of O1 could
correspond to, and possibly underlie, the Lagrangian density for bosonic string
theory, where the worldsheet coordinates are the coordinates which O1 can
observe. The present paper considers a fermion internal to O1, in addition to
O1's centre of mass. It is suggested that quantum mechanical uncertainties in
the transformation between O1's and O2's reference systems might require O2 to
use $d$ spinor fields for this fermion, where $d$ is the number of spacetime
dimensions. If this is the case, and if the symmetry/observability arguments in
arXiv:hep-th/0601104 apply, the resulting Lagrangian density for the dynamics
of O1 might resemble, or even underlie, superstring/M theory.
