Don't say the "S"-"H" word

I have to tell a story from the other week.  Alex is a cub scout and they meet with their pack/den a few times a month.  The last meeting they had they talked about manners and how to be a good scout.  They had to write them on the board, and Alex decided that - not saying bad words was a part of our good manners.  However, the way he expressed this was, "don't say the S-H word".  The other parents eyes looked a bit big and surprised.  So I asked Alex after the scout meeting, where did he hear the "S"-"H" word?  And he says, he said it before and we've yelled at him...hmmm...no I don't remember that!! So I asked him what word exactly did he say that got him in trouble before?  He made me promise I wouldn't yell at him for saying it, and I promised.  He said, "it's the word, SHut-up".  Oh my gosh, I couldn't help but hold back laughter.  Tisk, tisk on us adults - even when things look like exactly what we think...we could most certainly be wrong.  And geez, poor Alex, it can be tough to be a six year old!