Of course, it isn't really severed, it's just an illusion! What you are going to make is a special glove that will make it look like you are holding a living, moving, human arm. In actuality, what people are seeing is your hand, passing straight through a "dummy" glove with an attached fake stump of an arm.
While the project takes a few hours to make (or more, depending on your attention to detail), it is silly-cheap and has a great effect!
Step 1: Material list
*a pair of heavy gloves (I opted for dollar store work gloves)
*fabric (to be your "shirt" on the limb)
*a sheet of white paper
*some nice squishy foam
*a wire coat hanger
*blood colored paint
*some nice sharp scissors
*hot glue gun
*"Sculpey" or other clay that you can bake in your oven
The gloves that you pick are going to be the most important part of the project. Theoretically, you only need one glove- but the effect is best if you are wearing two matching gloves. You'll want to buy or find some that are thick, sturdy, and have longish cuffs. Having no extra gloves laying around, I bought mine for only a buck and they worked pretty well.
Every item besides the gloves I had around the house already, meaning a total cost of $1. If you already have some gloves that you could use, the project could be practically free!
Total time spent on this project was in excess of 10 hours, over the course of several days. This includes all the trial and error that you will be able to avoid, thanks to this Instructable, however! More than one day will be needed, to allow for the paint to dry. Time that you will require depends on how much attention to detail you take.