The legs were ereased by computer.
On Sat, 23 Jul 1994, Abigail Miriam Feder wrote:
> One effect from Forrest Gump I haven't heard discussed anywhere -- Gary
> missing legs. I know on stage such an effect is often achieved by actually
> taping the calf to the thigh at the knee, but in most of the shots of Sinise,
> the thighs looked too thin to have a calf taped to them. In the scene in
> he kicks the prostitutes out of his room, I thought I detected a flicker as
> hoisted himself back into the chair. Was the double amputation a special
> effect and if so does anyone know how it was done?