三个旅行者同时住进了一个旅店。早上出门的时候,一个旅行者带了一把伞,另一旅行者拿了一根拐杖,第三个旅行者什么也没有拿。晚上归来的时候,拿伞的旅行者淋得浑身是水,拿拐杖的旅行者跌得满身是伤,而第三个旅行者却安然无恙。于是前两个旅行者很纳闷,问第三个旅行者:“你怎知 Three travelers at the same time admitted to a hotel. In the morning, one traveler brought an umbrella, another traveler took a cane, and the third traveler took nothing. When returning at night, the traveler with the umbrellas was drenched with water and the traveler with his crutches was covered and injured, while the third traveler was safe and sound. So the first two travelers wondered, asking the third traveler: "How do you know