Laugh with the pupils when something unavoidably funny occurs; as, for
example, when a bird flying through an open window whizzes past a young
man at work at the blackboard, causing him to jump and make a wavy line
through his carefully drawn geometrical figure.
But be on the alert to discover mischief while it is being planned and
assign some interesting work in another direction.
Let it become a settled opinion of the pupils that you laugh when you
see a really good joke but that you do not laugh unless you see
something to laugh at.