The “King of Random” Grant Thompson shares how to make an exploding pumpkin face by capturing “a very flammable gas (acetylene)” in an already-carved pumpkin. You can view step-by-step instructions on Instructables.
I chose to ignite the gas with a pice of visco fuse. When the gas is ignited, the pressure inside builds rapidly, forcing the carved pieces to blast out dramatically. You could try making them this Halloween, but probably shouldn’t.