Short, quick warnings of danger can be very effective.

简短、快速的危险警告可以非常有效。

Too many " don't" and warnings of danger can make a child feel incompetent, fearful - and pessimistic.

过多的不许和危险警告会让一个孩子感到无能、胆怯——以至于悲观。

But as a communication device, it's a remarkably effective form of defense, able to send out complex messages warning of danger or distress.

但是作为一个通讯设备，它是个非常有效的防御工具，它可以发出警示危险或求救的复杂讯息。