However, there are also times when shipments circulate through the ports of many countries owing to the requirements of the transport ship. In such cases, to prevent the wily dealers from slipping away with the goods, it is necessary that each country along the route cooperate to keep the shipment under covert observation.
然而運毒的交通工具可能周遊列國，沿途經過好幾個國家的港口，必須提防狡猾的毒梟中途掉包，此時就需要沿途各國暗中密切監視。