 He said to him, I don't believe in you. I think the ghost is quite taken aback. Why don't you believe in me? And Scrooge's answer is basically, well, you could be caused by indigestion, for example. So essentially, you could be some sort of figment of my imagination that's caused by some kind of imbalance in my system, essentially. But Dickens used this far more humorous way of talking about it.