【英语时差8,16】立刻；（为微不足道的原因）动不动就…

This idiom has two different origins, resulting in two slightly different meanings. The first is that, before the invention of microphones¹ and loudspeakers², people at noisy sporting events needed a signal³ that was easy to see at a distance in order to know when to begin. One way to do this was to have an official at that event lift his hat high and then drop it. From this origin, "at the drop of a hat" means⁴ something done at a moment's notice. Some people are eager to do something they like very quickly "at the drop of a hat," if they get the chance.

Another origin of this idiom is that when two men were thinking to fight, one of them would throw off his hat. This was a signal he was ready to fight. From this origin, "at the drop of a hat" means something done for the slightest reason.

1 microphones   

n.扩音器，麦克风( microphone的名词复数 )

参考例句：

• They descended from the plane into a forest of microphones and cameras. 他们从飞机上走下来，迎接他们的是数不清的麦克风和照相机。 来自辞典例句
• The music was amplified with microphones. 音乐声通过麦克风被放大。 来自辞典例句

2 loudspeakers   

n.扩音器，扬声器，喇叭( loudspeaker的名词复数 )

参考例句：

• The loudspeakers blared the speech repeatedly. 扬声器里反复大声地播送那篇演讲。 来自《简明英汉词典》
• The vibrations are amplified electrically and can be heard through loudspeakers in the operating room. 这种震动通过电流放大后，就可以从手术室的扩音器中收听到。 来自辞典例句

3 signal   

n.信号，暗号

参考例句：

• This is a signal failure.这是明显的失败。
• A train must not pass a signal that is at danger.火车切不可越过危险信号。

4 means   

n.方法，手段，折中点，物质财富

参考例句：

• That man used artful means to find out secrets.那人使用狡猾的手段获取机密。
• We must get it done by some means or other.我们总得想办法把它干完。