In the presentation, this is an animated movie from the Mind Hacks book.

Okay… How did we do?

(This time a few people at the back got it after 10 seconds or so, and many more people saw the change as I narrowed it down. When I pointed out the actual change, the final third or half of the audience caught it.)

Matt Webb, S&W, posted 2006-07-14 (talk on 2006-07-13)