  The manner in which continuum center vortices generate topological charge
density is elucidated using an explicit example. The example vortex
world-surface contains one lone self-intersection point, which contributes a
quantum 1/2 to the topological charge. On the other hand, the surface in
question is orientable and thus must carry global topological charge zero due
to general arguments. Therefore, there must be another contribution, coming
from vortex writhe. The latter is known for the lattice analogue of the example
vortex considered, where it is quite intuitive. For the vortex in the
continuum, including the limit of an infinitely thin vortex, a careful analysis
is performed and it is shown how the contribution to the topological charge
induced by writhe is distributed over the vortex surface.
