Camping's 5/21 doomsday: What will the excuse be?

When Harold Camping and his followers find themselves still here after his doomsday deadline, what will his excuse be to explain it? *God changed his mind? *We prayed hard to give the sinners a reprieve and God granted it? *The calculations were off? *The devil did it? *We're not really here - you're just imagining us? .... What do you think the excuse will be?