Three Body Scattering" is a phenomenon that occurs primarily when large hail is forming in the atmosphere. Since the hail is so large and so reflective, a significant amount of the energy of the radar beam reflects off the hail and down towards the ground. The enery then bounces off the ground and again hits the reflective hail which again scatters the energy, part of which is received a second time by the radar. So instead of the hail producing a single radar return, it can produce multiple returns along the same radial as energy is bounced off the ground and again off the hail.

This causes a characteristic spike as shown in the image above angling off to the northwest and is known as a "Three Body Scattering Spike" (TBBS). The spike is not real in that the location of the spike doesn't really represent real hail in that location--however, where the spike begins can provide very valuable information as to where large hail is forming.