I agree with praetoritevong, but I want to make one point. People forget cards even when you ask them to remember them. Hell, I forget cards some times if I see more than a few card tricks near each other. For instance, when people do card tricks at our local magic club meetings, I write down the selection in the margins of my notebook (I'm club secretary, I write the minutes), because if I don't I'll forget the selection after seeing so many effects. When you use audience participation, you're putting the spotlight onto someone. You're making them part of the performance. That makes some people nervous. They are probably not performers, and they didn't expect to be part of the show when they got there. That can make it more difficult to remember what they need to remember. I agree that the people that forget cards, or didn't see the cards, are not hecklers. But don't assume that just because someone forgot a card they must have amnesia. This is why you have more than one person look at the card. Even Ricky Jay does this, and he's a great performer.