code: function( body ){
  
              var notify;
  
              // don't allow duplicates
              if ( this.has( body ) ){
                  return this;
              }
  
              body.setWorld( this );
              this._bodies.push( body );
  
              this.emit( 'add:body', {
                  body: body
              });
  
              return this;
          }
docs: chainable
  Physics.world#addBody( body ) -> this
  - body (Body): The behavior to add
  
  Add a body to the world