This is a trick that Matthew Weathers made for a lecture he presented in his Nature of Math class at Biola University. He apparently likes experimenting with mixing live action with video.
Here's his Halloween 2009 lecture:
How the heck did he do that?
I'm surprised that Biola (formerly the Bible Institue of Los Angeles) would allow him to use pagan halloween images.
I'm surprised the GrrlScientist would allow herself to use Biola images.