Whats a period

The kindergarten class had a homework assignment to find out about something exciting and relate it to the class the next day. When the time came for the little kids to give their reports, the teacher was calling on them one at a time.Eventually little Johnny’s turn came. Little Johnny walked up to the front of the class and, with a piece of chalk, made a small white dot on the blackboard, waited a short time and make a second small white dot next to the first.Well the teacher couldn’t figure out what Johnny had in mind for his report, so she asked him just what that was.’It’s a period,’ reported Johnny.’Yes, I can understand that,’ she said, ‘but what is so exciting about a period?”Damned if I know,’ said Johnny, ‘but this morning my sister said she missed one. Then Daddy had a heart attack, Mummy fainted, and the man next door shot himself.’