"As Laurent Benhamo started animating the jumping, falling horse in Maya, we realized the second pan from explosion to falling sand bags would need retiming and re-racking to achieve the most believable horse action. At all times we updated the animation scene with refined body tracks and refined camera moves. By the time we got the animation to a state we wanted to show Steven, Mark Osbourne, our TD lighting on the shot, had prepared renders that could be comped into the plate. With little time to finesse the comp Julien put the shot together for our first review. When we played it to Steven and his editorial team in LA and heard winces and shouts of 'OUCH!!' down the phone, we had apparently hit the mark."

The final section of the sequence involves Joey running into a number of barbed wire barricades strung between Belgian gates. The wire gets increasingly tangled around Joey until he is finally catapulted to a stop when the broken gates he has been dragging collide with an obstacle.

Working with Spielberg was like going to a master class everyday.

"For all of these shots we captured reference of the horse action using our witness camera array," Morris adds. "We also dragged practical broken gates behind quad bikes as visual reference for the FX artists at Framestore to match to when they attached CG versions to the real horses.

"As horse safety was our highest priority on set, all barbwire used near the horses was breakaway plastic, and the horses were never allowed to have any lengths of wire trailing from their body.

"Ben Loch, Julian Hutchens, Noah Taylor and Daniel Fernandez were our barbed wire team for the end of the sequence. Working in Maya and Houdini, and using a combination of nCloth and our in-house fBounce dynamics engine, they wrapped complex trails of procedural barbed wire around the body tracked 3D model of Joey and then tuned the wires reaction to give just the right 'springiness' to match the real wire reference we shot on set. Before starting the final shots we got Kevin Jenkins' team to paint static concept frames for key shots with varying levels of wire tangled around Joey's body. Following a review with Steven, we started rigging the dynamic wires based on the approved designs. Kate Windibank and Ben Aickin lead the comp team bringing the shots of struggling Joey to completion using a mixture of 2D elements and CG soil, debris and dust passes."

Morris concludes that working with Spielberg and his team (particularly production designer Rick Carter) was like walking into a master class every day of the week. "The hardest, but ultimately most satisfying aspect of the use of digital effects in this film is that our work is hopefully invisible to the audience," he says. "We've just finished shooting Steven's next film, Lincoln, in Virginia, ready to start post in the New Year."

Bill Desowitz is former senior editor of AWN and editor of VFXWorld. He has a new blog, Immersed in Movies (www.billdesowitz.com), and is currently writing a book about the evolution of James Bond from Connery to Craig, scheduled for publication in 2012, which is the 50th anniversary of the franchise.