A guy I know who does this uses cooked spaghetti as intestines and he uses liver as body organs. At the end of it all he has a sink to make sure everyone washes their hands real good. You can also use dry uncooked pasta as bones or teeth depending on the shape and size of the pasta you use. Packages of fake press on nails make...well great fingernails or toenails.
I'm not sure how it was rigged up, but there was one at a Halloween party I went to as a kid that I'll never forget. Someone was under the table with their hand up through a hole in the bottom of the box. I think they had some sort of glove on, too. When we stuck our hand in to feel around, they took hold of it. Talk about squeals and screams!
Okay here is one for everyone, we are adding soem new things to our fall festival this year. One thing we decided to add was a table with boxes that the kids put their hand in and touch what is in there (without seeing it). I know about unpeeled grapes, jello brains, slime, hair but am looking for suggestions. Anyone?
"When you stop learning you stop growing."