Fasten a candle or whatever you use to the bottom of a fish bowl with the modeling clay.
Fill the bowl with water. Add the citric acid and baking soda. Now add the mothballs.
This mixture keeps mothballs bobbing up and down for some time, Add more citric acid and soda when the action stops. Set the bowl on some greens and prepare to answer your friends surprised questions. Place netting(nothing solid) over top of bowl or jar, secure with pretty ribbon or tape to hold down.
A white crystalline powder used as a flavoring in food and beverages. Find it in the spice aisle or baking isle of your grocery.