Jif Jazz

There was peanut butter in the lost and found today.  In jazz band here, anything in the lost and found is fair game.  A few years ago, someone bought a PlayStation 3 game and put it, brand new, into that lost & found as a prank.  And today, there was a jar of peanut butter in there.  Unopened.  It must have been there all summer, because it's only the second day of school and the jar smelled terrible.  The peanut butter must have gone bad, and it can't have gone bad in one day.  I can't imagine how someone could get a jar of Jif into the classroom without someone noticing.  It was likely a prank, like the PS3 game.  Why else would someone have peanut butter in jazz band?