First... we used black Sharpies to decorated our film canisters to look like ghosts. SPOOKY!
Then... we mixed some water (about 1/3 of the film canister) and cornstarch (about 1/2 tsp) together in the ghost film canisters.
Last... we went outside (very important to do this outside), put a 1/4 piece of an Alka Seltzer tab in the film canister, put the top on the canister, and turned it top side down onto the ground.
... and now let's see all the fun!