The 1961 audience was totally wowed by the filming of TWO Hayley Mills in Disney's THE PARENT TRAP.   David Swift, director, was able to create the illusion of twins through the use of body doubles and a split screen. Ub Iwerk and Bob Broughton were the geniuses behind the new technological advancement in film. In creating the illusion of Hayley being her own twin, these scenes had to be filmed twice. Actress double, Susan Henning, stood in for placement during the filming of the split screen shots. Hayley would then, change clothes and wig for a re shoot of the opposite twin. Everything involved in the scene remained the same - camera, set, lighting, props, etc. for continuity. The other part of the screen is then filmed with the opposite - previously filmed - side which would be blacked out with a matte. The two strips of film were rephotographed one frame at a time. The 'split' in the screen is masked with a 'seam,' or background element - bedposts, door frames,