To investigate the origin of negative wakes in viscoelastic fluids, we used a perturbation method to calculate the flow induced by a solid sphere falling slowly through a viscoelastic fluid in a vertical column of square cross-section. The effects of normal stresses and inertia were determined by solving the perturbation problems numerically using a finite element method. The normal stresses give rise to a negative wake behind the sphere and a reversed flow at the front stagnation point.