A mother was anxiously waiting for her daughter's plane. She had just come back from a far away land trying to find adventure.
As the daughter was leaving the plane, the mother noticed a man directly behind her daughter dressed in feathers with exotic markings all over his body and carrying a shrunken head. The daughter introduced this man as her new husband.
The mother gasped in disbelief and disappointment and screamed, "I said for you to marry a Rich Doctor! A RICH Doctor!"
A witch doctor is a jungle equivalent of a doctor, but they don't use medicines as doctors do. The joke here is the similarity between the word witch and the word rich.
Shrunken is an adjective formed from the verb to shrink (shrink - shrank - shrunk). It means made smaller.
To gasp is to make a sharp sound because you breathe in very quickly and suddenly in surprise.