  We discuss the origin of spin correlations observed in neutron scattering
experiments on the paramagnetic phase of a number of frustrated spinel
compounds, most notably ZnCr2O4. These correlations are striking for two
reasons. First, they have been interpreted as evidence for the formation of
weakly interacting hexagonal clusters of spins. Second, they are very different
from those calculated for the nearest neighbour Heisenberg pyrochlore
antiferromagnet, in which Coulomb phase correlations generate sharp scattering
features known as pinch points. Using large-$n$ calculations and Monte Carlo
simulations, we show that very weak further neighbour exchange interactions can
account for both the apparent formation of clusters and the suppression of
pinch points.
