This is a quick instructable on how to make a very realistic severed finger prop for Halloween. I used to do this in McDonald's back in the day when styrofoam containers were used. More than once I was able to get a scream out of the cashier when I revealed why I was demanding a refund!
Step 1: Buy Some Finger Food
You'll need a box for holding fast food to pull this off right. One of the folding containers from Jack-in-the-Box was used for this one (thus the name) but my favorite choice are the old-school foam boxes from McDonald's. You should get some chicken nuggets, or other "finger food" to further the humor of this little gag.
Step 2: Extra Ketchup, Please
Also make sure to get a few packets of ketchup. One or two packets should provide a sufficient volume of fake blood.
Step 3: Cut Out a Hole
Empty the box and cut out a small hole near the corner of one of the hinges. Make this on the right side if you plan to hold it with your left hand or the left side if you plan to hold it with your right hand. (This will make sense once you move forward.)
Step 4: Insert Finger
Now you should be able to insert your finger into the hole you made. the fit should be snug to prevent the ketchup from flowing out the bottom.
Now you can bend your finger down while holding the box to make it look like a severed finger laying down in the box. (Now the position of the hole should make sense to you.)
Step 5: Gild the Lily (with Ketchup)
Open one of the ketchup packets and squirt the condiment all over the seam around the hole where your finger is coming through. Place the nuggets (or your finger food of choice) randomly around the finger.
Step 6: Scare the $#!+ Out of the Cashier
You may now present the box to the cashier with the lid closed. Briefly complain about wanting a refund while opening the box in your hand. The reaction you get will stay with you for the rest of your life :-D. You can also wiggle your finger just a little to give it life. Bon appetite!