How does a Boomerang return?

• 'Boomerang' is the hunting weapon of the Australian aborigine. 

• It is a curved piece of hard wood, about 2 ft. 6 inches long. 

• It is flat on one side and rounded on the other.

•  A slight twist in the angle of one of the 'wings' makes it return to the owner when thrown.

•  But when it hits something on the way, it cannot return. Special non-returning types are made for use in warfare.