A small white dot!

A kindergarten Class had a homework assignment to find out something exciting and relate it to the class the next day.
When the time came to present what they'd found, the first to the front of the class, and 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,' chirped the little boy, 'but this morning my sister was missing one, my mother fainted, my dad had a heart attack, and the boy next door joined the Navy.