Frenchmen in the know would place a paper fish on the back of ignorant revelers, calling them " poisson d'avril" or " April fish."
知情的法国人会将纸鱼放在不了解情况的人背上，叫他们“四月鱼”。
英语百科
Fishpaper
Fish paper or fishpaper is a strong, flexible, fibrous dielectric paper. It resists moderate heat and mechanical injury, and is often used for wrapping coils and insulating stove-top parts. It is hygroscopic and so must be treated with paraffin for use in moist environments. Some fish papers incorporate mica layers to increase the dielectric strength while still giving good mechanical strength.