Magic

• The film's infamous teaser was a single slow zoom into Fats' face while the dummy recited the tagline poem: 'Abracadabra, I sit on his knee / Presto-chango, and now he is me / Hocus pocus, we take her to bed / Magic is fun; we're dead.' The spot scared kids badly enough that it spawned a long-running legend that it aired exactly once before being yanked after parent complaints.
• Anthony Hopkins was allowed to take Fats home to rehearse and got so rattled he phoned the production's ventriloquism consultant in the middle of the night, threatening to throw the dummy into the canyon if someone didn't come get it. Attenborough personally went over to calm him down.
• Jack Nicholson was offered Corky and turned it down, reportedly because he didn't want to wear a hairpiece for the part.
• William Goldman adapted his own novel: producer Joseph E. Levine bought the book in March 1976 for roughly $1 million, with Goldman attached to write the screenplay.
• Gene Wilder was the first choice for Corky and both Attenborough and Goldman wanted him, but Levine refused, insisting on no comedians who might undercut the serious tone. Attenborough took the directing job partly on Levine's promise to bankroll his long-gestating Gandhi project, a promise Levine later broke.
• Ventriloquist Dennis Alwood, a friend of the legendary Edgar Bergen, designed, voiced and operated Fats and tutored Hopkins, who trained in both magic and ventriloquism for the role, though the marketing pushed the idea Hopkins did it all himself.

Fats isn't supernatural at all. He's the part of Corky that gets to be confident, vicious, and wanted. Every 'possession' beat tracks a moment Corky can't face directly, the dummy says the unsayable, then commits the act Corky needs done. The horror is a personality split given a wooden mouth, not a haunting.

Read it as a story about performance eating the performer. Corky only succeeds when he stops being himself and lets the act talk. By the Catskills, there's no Corky left underneath, only the routine running on autopilot. The lake retreat is a man trying to find the self he traded away and discovering it's already gone.

Peggy Ann Snow is less a love interest than the one piece of Corky's pre-fame life he thinks can save him. He goes looking for the boy who loved her, but Fats has to die for that boy to exist, and they can't both survive. The tragedy is that Corky chooses the act over the only future where he stays human.

Corky is a failing magician until he hands his act over to Fats, a foul-mouthed dummy who carves the room open with the cruelty Corky can't voice himself. On the verge of a network TV deal that requires a psych eval, he bolts to the Catskills and the high-school crush he never got over. Out at the lake, Fats stops being a bit. The wood does the deciding now, and the people in Corky's orbit start turning up wrong. Attenborough plays it as a slow strangulation of one man's sanity, with the punchline already grinning on his lap.