The Thing That Wouldn't Die (2) - S6-E20
Corrected entry: At the end of the show the aliens leave and Dick chops Mary's neck to supposedly help her forget he ever existed. However, what about all the others? It makes no sense to make Mary forget them when everyone else would still remember them. How could she explain not knowing Dick when she would invariably have his stuff around or hear others talking about them?
Correction: Dick only erased Mary's memory because she was torn between her love for him and her desire to stay on Earth. It had nothing to do with making sure no one remembered them, just to hopefully help Mary move on with her life.
Bishop73