I'll show you how I made a keg tap for Halloween where you stab a head to pump the keg.
Step 1: Materials
Severed prop head
2 coupling nuts (size may vary)
3" threaded rod (matches coupling nuts)
Grinder, sander, or sand paper
Welder or JB Weld
Step 2: Head Preperation
Cut a hole in the bottom of the head large enough to go around the tap, and a hole in the top for the knife to pass through.
Remove the stuffing so nothing interferes with the pumps operation.
Step 3: Knife Assembly
First and foremost, dull the blade. We don't want real blood used for the project. I used an air grinder to do this, but you can use any method you'd like.
Next, remove the ball off the tap. Screw both coupling nuts onto the threaded rod, leaving enough room on one end, so you can screw it onto the tap.
Lay out your coupling nuts onto the knife, and secure to the blade either by welding or with JB weld.
Step 4: Final Touches and Assembly
Push the tap through the head and screw the knife onto the tap.
Use a zip tie to secure the head to the tap.
Tap the keg and stab the head!