What happened to the inventors body?

I assume, Edward probably buried him in the garden.
about his knifes for fingers part, my theory is, Edward probably dragged the inventor by maybe his leg by clasping his two hands together over his leg and dragging him. I know this seems like an odd theory, but it would make sense and Edward had all the time in the world to drag him for days.

Well.. Being that the inventor was Vincent Price, so I have to assume the body turned into an enormous bat or raven and took to the night sky.

But that's another bedtime story for another night.

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As with many things, your mileage may vary.

Why would Edward have any concept of moving or burying a body?

It probably would've been a bit too dark for this movie, but I would've liked to have seen Peg stumble across Vincent's remains while snooping around the mansion; maybe instead of having her find that collage of clippings in the old fireplace, she could've found the King of the Grand Guignol's old bones enshrined there instead.

A Superman without trunks isn't worth watching or reading about.

I assumed the police discovered him dead at some point. I don't know if he distributed his cookies but his suppliers not receiving their shipments could have tipped off that something was wrong. And who knows if he had invented machinary for other people and companies. When communication stop perhaps someone made the call to the police to check it out. Or he just stopped paying his bills and the police gave it a visit that way.

Well the Inventor never really made a scissor boy, he may have never even exists.
What we are seeing the the story Kim is telling her granddaughter, a made up story adults tell kids, bedtime stories.