 When Ms. Dewitt asks Curtis if the sheep are on the roof, it is a  reference to a prank in which one would let four sheep out on the  school roof and have numbers spray painted on them. The number are  1,2,4, and 5. When the administration of the school lets the sheep  down, they’d be searching for days to find the 3rd sheep that  doesnt really exist. Unfortunately, Big Fantastic was unable to get  actual sheep for the episode.