Shu dog barks at the sun.
Shu 蜀 is the abbreviation for Sichuan 四川 in China. The province is usually damp and foggy. The dogs there do not know what the sun is. Once in a while, the fog clears and the sun appears but the dogs there behave as if they see UFO. One dog starts to bark and many others follow.
There is another proverb: 一犬吠影 百犬吠聲 which translates into "One dog barks at a shadow. Hundred dogs bark at the noise."
When one dog starts barking because it sees a shadow, many other dogs join the chorus and bark just because they hear someone barking.
Does this sound familiar to you?