 CONT: At the Town Hall meeting, just as everybody starts moving from  the corridor into the council chambers, the blackboard at the back  of the room is clean. It remains clean in some shots later during  the meeting, but when Quint scratches it before his first tirade,  there is a large shark, water and all, drawn on it in white chalk.  No one was seen drawing it, nor was there time for anyone to draw it  during the few seconds between the last shot when the blackboard was  seen clean and the shot of Quints nails scratching it.