you could have heard a pin drop idiom
（因着迷或惊讶而）鸦雀无声
something that you say in order to describe a situation where there was complete silence, especially because people were very interested or very surprised by what was happening
Margaret's ex-husband turned up at the wedding. Honestly, you could have heard a pin drop. 玛格丽特的前夫出现在婚礼现场。老实说，当时全场真是鸦雀无声。