Dunno if it counts as a party trick, but it's kept my nephew Oli quiet on many occasions:
You interlace your fingers so that they end up down between your palms (not on top of your hands as is the more obvious way to do it), and put your palms together, with thumbs side by side. This is the church. Raise your index fingers to a point, this is the steeple. Open the door (move your thumbs and palms apart and turn to whole thing 'inside out', and there are the people (your fingers wiggling). Oli now knocks on the thumb 'door'. And for some reason, then weaves his finger among the 'people', saying it's a snake, or sometimes an elephant. I think he was amused by my idea of the vicar having to get a bucket for the poo...
The 'trick' of course is interlacing the fingers the right way - do it wrong and you can't turn your hands 'inside out' and there aren't any people. Small children take a while to pick that bit up, so they struggle to emulate it.