What is the most interesting fact you know about dolphins?

Question: What is the most interesting fact you know about dolphins?
- Keywords:
  dolphin,
  fact,
  interesting
Asked by kateemily to Valeria on 13 Jun 2012.
- Valeria Senigaglia answered on 13 Jun 2012:
  
  When two groups of killer whales meet in Washington State, USA, they have a greeting cerimony with stereotype behaviour!
  
  Beluga whales makes underwater air bubbles for fun.

Question: What is the most interesting fact you know about dolphins?