It's a magical and wonderful experience to be a teacher of non-native English speakers at an international elementary school on April Fool's Day, the specific reason being that while the kids are enthusiastic about the suddenly called-for trickery, none of the them actually understands why or how it works.
In my ESL class, my student Polina was quick to point out, "Teacher! You have spider on your head! Hahahahahahaha!" This was followed by a prolonged silence in which my students stared at me, faces taut with the anticipated rapture of a prank well pulled, with me finally exclaiming, exasperated, "You have to say 'April Fool's!' afterward or it doesn't count!" It would help if any of them understood what "fool" meant, or how to even spell it, but mostly it comes out like the first syllable of "foosball."
Cindy left her 6th grade English class to find a note secretly placed in her pocket that simply read, "eat my tshirt happy all fools day."