A kindergarten class had a homework assignment to find out something
exciting and tell it to the class the next day. When the time came to
present what they'd found, the first little boy the teacher called on,
walked up to the front of the class with a piece of chalk, made a small
white dot on the blackboard, and sat back down.
Puzzled, the teacher asked him what it was.
"It's a period", he replied.
"I can see that", said the teacher, "but what is so exciting about a
period?"
"Darned if I know" he said, "but this morning my sister was missing
one, my mom fainted, my dad had a heart attack, and the boy next door
joined the Navy."