 When the shark attacks Hoopers cage, theres live footage of a real  Great White with a rope hanging from its mouth. This sharks mouth  is clearly much smaller than the sharks mouth when it attacks the  boat moments later. These scenes were filmed by noted shark  photographers Ron Taylor (VI) (qv) and Valerie Taylor (I) (qv)  specifically for the movie. Because the Great White sharks they  filmed would be smaller than the mechanical shark in the movie, they  constructed a smaller version of Hoopers shark cage. Inside the  cage they alternately used a small mannequin or a little person. One  of the sharks they attracted got caught in the cages cables and  tore it apart trying to escape. The footage was so good that they  changed the script to reflect the destroyed cage and Hooper escaping  by hiding on the ocean floor. However, the small person used in the  scene refused to go back in the miniature cage, which was damaged in  the incident.