How to make a sweet smoke ring cannon!
This is the coolest damn thing.
Take a bin, just your average ~1 ft high plastic bin, it can be round or rectangular. It just needs a flat bottom and a mouth you can easily fit material around. Now cut a circular hole about 5 inches in diameter in the bottom in the centre. Take a shower cap or similar fabric/plastic liner and {tape it/elastic band it} over the fat open end of the bin.
Now comes the fun part, get something that will generate nice thick smoke, like say a tin box with burning paper or something in it (you can buy little smoke makers - CAREFUL don't burn your house down). Put them in the bin for a couple of minutes to let it fill with smoke.
Now pick up the bin, aim and tap the fabric on the fat end...hey presto, you get a nice tight smoke ring.
If you do it right, and I've seen it done in a lecture, you can get smoke rings to fly 10-25 feet and stay in the air for 30 seconds...you can even shoot rings through other rings etc...endless fun