April Fools!
Apparently April Fool's Day is a huge day in France. During my first class today, a bunch of my students from a different class barged into the room and paraded around it clapping, chanting, and shaking random students' hands. They only stayed about a minute, so I just let them carry on, watched them leave, and then commented to the students in my class at the time that it had been a very interesting experience. One of the girls responded, "It's the first of April!" Suddenly I understood what had happened, and I witnessed several more jokes throughout the day. In my last class this afternoon, I played a joke on the students. I waited until they had all come in, taken their seats, and settled down. Then I stood up and said in English, "We're not having class today. You can all leave." A couple of the students looked a little surprised, but most of them made no reaction to my comment whatsoever. So, I asked in French if they'd understood, and they all said, "no." I repeated in French, "Il n'y a pas de classe cet apres-midi; vous pouvez partir." Then they all got excited and jumped up, exclaiming, "vraiment?!" ("really?!") Then I shouted, "April Fool's!" over all the noise they were making. It was quite funny; I think they appreciated my joke.