As they have a normal conversation, the kids are not allowed to use the letter B. I don't know why they chose B, although there was one day when another letter was chosen (I think it was F that day). If one of them says a word containing said B, all the others in the group get to sock him/her in the arm (hence why I frown on this game in class).
If, however, the person realizes that he/she used a B somewhere, if he/she immediately says, "baby bridges," the B is erased, and no hitting occurs.
I wonder about things like this. Where did it come from? How long have they been doing it? (I don't recall noticing it before this school year.) How widespread is the adoption of the game?
I'll be keeping an ear out for random "baby bridges" from now on. I wonder how long this fad will last.