The head tails of a twi'lek, known to them as Lekku or Worms to other races, are often the pride and joy to most people of Ryloth.
Long lekku are usually a sign of health, sexual potency and therefore status.
Oola's lekku, being longer then normal helped to make her very popular on her homeworld. Every male, and even some females, enjoyed watching them swing and move with each delicate step she took.
When Bib Fortuna saw her long worms swinging through the air he knew he had to have her. He considered keeping her for himself until he realized her dancing would make the perfect gift for Jabba.