Svengali Magic Cards are the madnotes! All they are is a deck of playing cards consisting of 24 ordinary cards (all different) and 24 duplicate cards (all the same). They are arranged alternately throughout the pack so a duplicate card follows an ordinary card and so on. The genius is this, the duplicate cards are minutely shorter than the ordinary cards which means that if you rifle through the cards one way you can show a spectator that all the cards are different because they will only see the ordinary cards as the pack is flicked through. However, if you rifle through the pack the opposite way, only the duplicate cards will show, making it seem that the whole deck is made up of the same card!
10 minutes of practising how to handle the deck and you're ready to perform endlessly simple but amazingly enthralling card tricks!
I bought my pack some 2 years ago when I was in Hamleys in Regent Street London and one of the staff was demonstrating them. You only found out how he was doing all these amazing tricks if you actually bought a pack, and no amount of pleading would get him to talk otherwise, so I shelled out £6 to know the secret.
I've just come across them again after clearing out our loft (attic) and I'm planning on freaking out my stoner friends during a session, seeing as I've already frazzled their brains with the Doomsday algorithm.