 To achieve the effect of cars sliding into each other when hit by  the patrol car at Moran Cadillac, the filmmakers put oil under the  tires of the first few cars to help them slide. When it came time to  do the stunt, it worked too well and many of the agencys own  Cadillacs that were for sale were badly damaged. Director  H.B. Halicki (qv) had to purchase all of them.