A very smart dude by the name of Mark Rober figured out that if you strap two iPad 2's to yourself, you can create this incredible, freaky hole effect. This guy should work for NASA. Oh wait, he does.
It's really pretty simple. You strap one iPad 2 to your front, one to your back, and you start a FaceTime chat between them. That's basically it! Cut a couple holes in a shirt, add some fake blood, and you're done. He even adds that if the party you're going to has crappy Wi-Fi (or if you're going to be roaming the street, trick or treat style) you can just carry a portable Wi-Fi hotspot in your pocket.
Mark is a Mechanical Engineer for NASA's Jet Propulsion Laboratory. He was part of a large team that just finished working on designing the next Mars Rover (called Mars Science Laboratory) that will launch around Thanksgiving. I asked him what exactly he did on it, and he said he's, "spent the past 5 years designing and delivering hardware on the Sky Crane (the thing the Rover gets lowered from when it reaches the surface) as well as some hardware that sits on the top of the Rover top deck that acts as an interface when the Robotic Arm comes to deliver a sample of dirt into the belly of the Rover to test for traces of organics." Yeah, then in his spare time he thinks up a halloween costume that's way cooler than everybody else's. Nicely done, sir. Nicely done.
And yes, iPad 2's are expensive, but if you've got one, you can always just borrow another from a friend. Or borrow two. Or use two phones for a hole in your head. The possibilities are endless.