I'm about to post another instructable. I was playing with a audio driven skull I built last year, mostly from this site:
http://www.scary-terry.com/audioservo/audioservo.htm
I added a pre-amp and a mic to the project there, and I made it work off of a USB battery (which was the hardest part, actually, because those things have an auto-off you have to defeat without burning up all the power in the battery.
So I figured, why stop there? I made it into a full costume with false shoulders and arms. I was going to do mechanical hands, but I didn't have enough spare parts for that, and the objective was to buy nothing new except glue sticks. So now I've got an 8' tall grim reaper costume with like a 10' wingspan with a skull that opens and closes with my voice. Originally, I had the arms extendable using drawer rails from an old Ikea dresser, but I had to get rid of those. They're not very strong outside of the dresser, and I slung one to pieces trying to open the arms Wolverine style. Because the best feature was that the rails were designed to lock closed normally. But after vacuuming up ball bearings, I decided I'd just use static arms. Will post soon, but in the meantime, here's the diagram I made for the costume frame:
EDIT: And yes, I had all those PVC pieces sitting around from a previous project. It was a mosquito net frame for my son's boy scout camp, but he never used it. He didn't even take it the last 2 years.