Contagious laughter

A teacher was working on English assignments with her class, when she asked each kid to come to the front and use a word she gave them in a sentence.

The kids went up one by one, and everything was fine, until teacher called on little Billy.

Billy went to the front and the teacher said

"Billy, your word is contagious"

Little Billy scratched his head and thought for a while, then smiled and said

"Mummy said Daddy is going to redecorate the entire house, but it will take the stupid contagious"