The secret sauce of 'Who Framed Roger Rabbit' is not a single trick so much as a whole machine of careful, nerdy craftsmanship working together. I love how the film treats cartoons like physical actors — the team started by shooting the live-action plates with actors reacting to empty space, eyeline marks, and clever stand-ins. On set they used rigs, props, and sometimes puppets or cardboard cutouts so the lighting and interactions would register correctly on the human performers. That meant Bob Hoskins and the others could touch a table or hand off a prop and make it feel real even though the cartoon wasn't there yet.
After the live footage was locked, animators led by Richard Williams took over. They hand-drew each frame of the toons to match the timing and camera moves, using exposure sheets that laid out exact frame counts and cues. To blend the drawings into the film, the team photographed ink-and-painted cels and then optically composited them over the live-action negatives. For shots with camera movement they used motion-control techniques so the animated layers could follow the same perspective and parallax as the live camera. Shadows, reflections, and interactions were painstakingly hand-crafted — sometimes animators painted shadows or reflections frame-by-frame; other times they created mattes and used multiple optical passes to get the lighting to sit right.
What I always admire is how every tiny detail mattered: a cartoon's shadow had to land with believable softness, a splashed coffee needed animated droplets that
matched live water, and timing had to sell the comedy. The result feels alive because the filmmakers respected both cartoon physics and photographic reality, and their respect shows in every laugh and touch. It still feels magical to me.