if the back project image could be detailed, it would be a cool idea to have a grotesque version of whatever the front pattern was, for example....
little girl on front - zombie girl on back
nemo on front - jaws on back
funny grinning jack - zombie pumpkin come to eat BRAINS!
I'd love to try that, if there were patterns and a possible 'how-to'
if you are reading this then you are blissfully unaware of what is creeping up behind you...