An elementary school teacher gave her class an assigment, to go home and think about something that is interesting to them and be prepared to tell the class about it the next day.

When it was little Bobby's turn to speak, he went to the blackboard and drew a small white dot with chalk and then sat back down.

The teacher ask Bobby if that was a period.

Bobby replied yes.

She then ask Bobby what was interesting about it.

Darned if I know, but my sister is missing hers which made mom faint, dad have a heart attack, and the boy next door join the Navy.