April 1 In sixteenth-century France, the start of the new year was observed on April first. It was celebrated in much the same way as it is today with parties and dancing into the late hours of the night. Then in 1562, Pope Gregory introduced a new calendar for the Christian world, and the new year fell on January first. There were some people, however, who hadn't heard or didn't believe the change in the date, so they continued to celebrate New Year's Day on April first. Others played tricks on them and called them April fools. In France today, April first is called Poisson d'Avril. French children fool their friends by taping a paper fish to their friends' backs. When the young fool discovers this trick, the prankster yells Poisson d'Avril!
16 世紀的時候，法國人是在4月1號慶祝新年的。他們那時候過新年的方法和我們現在幾乎一樣，人們設宴、跳舞直到深夜。到了1562年，教皇格裡高利頒布了基督教新曆，按照新曆，新年這一天改到了1月1號。但是，有些人沒能聽說或者聽說了但不相信新年改天了。他們還是按照老習慣在4月1號這天過年。其他人就拿他們開玩笑，把他們叫做「愚人」。如今，法國人把愚人節叫做「上鉤的魚」。法國孩子會在朋友的背上貼一條魚，以此來戲弄別人。當那個受騙上當的小朋友發現以後，開玩笑的人就大叫「上鉤的魚兒」！
Today Americans play small tricks on friends and strangers alike on the first of April. One common trick on April Fool's Day, or All Fool's Day, is pointing down to a friend's shoe and saying, Your shoelace is untied. School children might tell a classmate that school has been canceled. Whatever the trick, if the innocent victim falls for the joke the prankster yells, April Fool!
如今，每逢愚人節，不管對方是否相識，美國人都會開些小玩笑。在愚人節比較常見的把戲是指著別人的鞋子說：「你鞋帶沒系。」學生可能會騙同學說學校放假了。不管是什麼樣的招數，只要那個無辜的受害者中技了，惡作劇的人就會尖叫：「愚人!」
Most April Fool jokes are in good fun and not meant to harm anyone. The most clever April Fool joke is the one where everyone laughs, especially the person upon whom the joke is played. American humorist Mark Twain has said that the first of April is the day we remember what we are the other 364 days of the year.
愚人節開的玩笑基本都是挺逗人的，沒什麼惡意。最高明的愚人節玩笑能讓在場的每個人都捧腹大笑，即使是那個被作弄的人也會忍俊不禁。正如美國幽默作家馬克吐溫所說的「只有在四月的第一天，我們才記起在過去一年的364天中我們是多麼的愚蠢」。
在英國，有一句關於愚人節的俗語：
「Fool me once, shame on you. Fool me twice, shame on me」
騙我一次，是你不對；上當兩次，是我不對。（也可以理解為「吃一塹長一智」）
But fool me three times, it must be April Fool's Day
上三次當，原來今天是愚人節。
可見在國外，愚人節已經形成了一種氛圍。
在愚人節那天，除了Fool這個單詞，Prank（整人、惡作劇）更加常用。
I was/got pranked! 我被整了！
To fall for a prank！我被整了
A prankster！愛搞惡作劇、愛整人的人！
還有一個很常用的短語，就是 「 pull sb's leg」意思是開某人玩笑。如果對方成功的上了你的圈套，在你感受了整人的喜悅之後，可以這樣說：
I'm just pulling your leg！逗你玩呢~
I'm just messing with you！開玩笑呢，哈哈