I remember in one episode, down in the lab, Grandpa is making something and a HAND comes out of a box I think and hands grandpa something and he says, "Thank you"

It's been a while since I saw that, so I may not be getting all the details right, but that's generally what I remember.

I wonder if this was done with thing from the Addams Family in mind? I wonder if the Munsters were originally going to have a "hand" type creature living in their home as well