you went to class and found a note in the desk that said "Hey there fellow student!! You found me! :)" it had a little shark drawing next to it. It must be a student from a different class period...you wrote on it yourself and put it back where you found it and the next day you went back to that class to find that the person had wrote in it again

"Woah hey, somone actually found it!! What period are you in??"

you write back