April Fool's Day: Ideas for pranks

Our son's class was specutating about pranks their teacher could play on them for April Fool's Day. Two interesting ideas:

Idea 1: Give students squids with the ink-part intact, so that they get squirted with ink. (I'm not sure if anyone other than a teacher of a parent can appreciate the difference between an idea like "squirk ink on them" and "use an unclean squid so that they get squirted with ink". I find this to be a thoughtful and educated prank for a group of 8-year olds.)

Idea 2: Give them square-root problems to solve and tell them to do them in their heads, but choose ones are can't be done in their heads. Then watch them struggle. (I don't think I knew about square-roots when I was 8.)