In an elementary 3rd grade class the teacher asks  each student to come up to the black board and write something exciting they have come across during summer holidays.

. one boy draws a mountain peak and says hiking was exciting
. another boy draws a zig zag line and says he saw a big lightning and it was exciting
. this boy goes up, just draws a dot and goes back to his seat.    

Amused and confused, the teacher asks what is it did you write?    
The boy says a period
Teachers asks what is so exciting about a period
The boy says when my eldest sister missed one, there was excitement in the house!