It has to do a lot with this thread - https://bitcointalk.org/index.php?topic=67739.0
This is the explanation I gave when I was at the Israel Bitcoin Meetup
Imagine you play poker with your friend... Both of you have stack of chips... During the game you stack of chips grows\shrinks... When you done you change chips into cash and go..
Now imagine you play with Bitcoins instead of chips...
Pot = 2-of-2 multi signature transaction ( tx A)
After each round you (you and your partner ) create transaction ( 1 input(tx A) and 2 outputs ) (don't transmit into network ) representing your bitcoins if the game will end right now.
When game is over and you want to cash out - you send latest transaction to network...
Is it clear now?
Now apply it to oneway bitcoin movement from client account to girl's account...
If we manage to do this software - in 2 years all webcams will be working like this.