源于欧美旧时习俗。这一比喻带有鲜明的民族色彩。在西方文化里，英美人大多讨厌老鼠。他们在形容“湿”的时候，常用被淹的老鼠来比喻，as wet as a drowned rat跟汉语中所说的“湿得像落汤鸡”类似。

【例句】
After raining cats and dogs he is as wet as a drowned rat.
倾盆大雨过后，他像落汤鸡似的。

Walking in the rain for an hour, Mr. A was as wet as a drowned rat.
先生在雨中走了一小时，湿得像落汤鸡。