You'll need a few things to get started: A large bowl, a small fountain pump with a short length of tubing, and a small plastic container. I used an old pump I had laying around and an old CD spindle. Remember that the container must be big enough to hold the pump, but small enough to fit well into the bowl. Any container will do, but I did find that the CD spindle cracked easily when drilled in the next step. You will also need some filler material. I used aquarium stone, but you could use just about anything. You could use sand, but extra care must be taken to ensure that it is not ingested by the pump. Finally, you need your pumpkin. The one I used was hollow blow molded plastic with a light in the back. Last, you will need some blood. Many stores sell fake blood in large bottles, but you won't want to use too much. Fake blood is often very viscous and little fountain pumps may not like it. I diluted my fake blood with water.
Step 2: Fun with a drill
The purpose of the small CD spindle is to allow the blood easy passage to the pump through the stone. Depending on your fill material, you may find that the intake of your pump does not have enough surface area to allow the blood to filter through. Drill lots of holes through your container. Use a bit that is just smaller than your fill material. I found that the holes shown in the picture were not enough, so you really need to drill a lot. You will also need to drill a hole in the top of the container for the hose, and a slot near the lid for the power cord. When you're done, toss the pump in that bad boy and you're almost done.