The coin is slapped against the bottom of the bottle and flys into the bottle like a... bullet.
It is possible to borrow the bottle, the coin, and perform a signed version of Bullet. All of this is taught in detail by acclaimed master Justin Miller.
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This is fairly impromptu, but not quite as much as they say. I'd say 90%. Justin goes over the handling and technique with your own coin or borrowed very very well. He explains everything in detail and helps take away your fear of being caught. Now there is a certain risk with everything but if you practice enough you can be very convincing. I think if you are trying to get into coins this would be a good first buy to help you have a very good effect to build your experience and confidence, and help you settle in.
Justin explains a number different ways to seemingly make make a coin go in a bottle when you have a borrowed coin or a borrowed bottle. He also has a scenario that uses a gimmick and goes over angles very well.
"Borrowing" the bottle and coin isn't really what you think it is. I mean, technically you do, but...
The effect itself it well thought out though, and the handling is great. It's also very visual, and therefore produces great reactions.
The only reason I dropped a star was the fact that it isn't as "spur of the moment impromptu" as I expected and I don't think it's practical for street performing: having a bulky bottle with you at all times, forcing a spectator to drink their beverage quickly to get a bottle, having to plant a bottle, needing an extra coin, etc.