The special ability reflective spell resistance of the nerra says
A nerra has a special type of spell resistance that causes any targeted spell it successfully resists to bounce off and reflect back at the caster. The caster becomes either the spell’s target or the point of origin for the spell’s effect, as appropriate. In addition, nerras are immune to gaze attacks, and such an effect is reflected back to its origin. (Fiend Folio 127)
If a caster casts the spell vampiric touch and hits a nerra but the caster fails to overcome the nerra's reflective spell resistance, what happens? Who gains temporary hp and who loses hp?