The $D=11$ pure spinor superparticle has been shown to describe linearized
$D=11$ supergravity in a manifestly covariant way. A number of authors have
proposed that its correlation functions be used to compute amplitudes. The use
of the scalar structure of the eleven-dimensional pure spinor top cohomology
introduces a natural measure for computing such correlation functions. This
prescription requires the construction of ghost number one and zero vertex
operators. In these notes, we construct explicitly a ghost number one vertex
operator but show the incompatibiliy of a ghost number zero vertex operator
satisfying a standard descent equation for $D=11$ supergravity.