Take A Laugh

Little Johnny asks his teacher: Excuse Ma, if you mix Omo detergent and klin detergent, will there be foam?
Teacher responded: Yes of course, why ask such a stupid and senseless question at the beginning of the year, are you going to pass this class at all?
Little Johnny laughs and whispers to the other kids, what a dumb teacher!, how can you get foam when you mix Omo detergent & Klin detergent without adding water, are we going to know anything at all with this teacher.