I 'invented' this in RE and I'm sure others have done it before but mine requires no water and no materials other than the bottle
this is my first instructable by the way so I made a simple amusing one.
Anyone who put's grandad's eye out or anyone else's eye out or damages them in some odd way with idea takes full responsiblity by using this information to create the item and effect ilustrated
Step 1: Put the Bottle Under Pressure
The best way of doing this is bending it in half or crushing it down as much as possible untile the bottle is too hard to squeeze
Step 2: Firing the Cap
the cap should be just tight enough to hold pressure wrap thumb round the cap and in one smooth flick spin the cap off of the bottle it will fly away with a satisfying pop
another variation is to leave that 2/3 full fizzy drink for a little bit longer and flick the cap off, you'll be left with vapour flowing out of the bottle.
2/3 full bottle of fizzy water? shake it hard for 30 seconds and fire, it sounds like a gunshot and the cap will have much more velocity than the others
also if you're getting a drink it looks really cool to spin the cap off into your hand (this one is for still drinks