I noticed this colour changing card trick today that I feel would be useful for sessions demonstrating concepts related to visual perception.
There was another one floating around Youtube a few years ago (has been since removed) and I was surprised to learn that a lot of people hadn’t seen it. Follow the instructions carefully and then watch the video.
1) The video lasts only about 20 seconds.
2) It is CRITICAL that you focus completely for the twenty seconds to get an accurate result.
3) The objective is to COUNT HOW MANY TIMES THE BALL IS PASSED BETWEEN THE PLAYERS IN WHITE SHIRTS.
4) This can be tricky since the players in black are only there to distract you.
6) Do NOT count the number of times the ball is passed between the players in black.
7) In other words, IGNORE the people in black shirts.
8) Do NOT read any comments on this post UNTIL you watch the video and post an answer. (Reading posts first may bias your results.)
9) Do NOT attempt to cheat by pausing frame by frame. Let the video play ALL the way through.
Now, watch the video on this page (it is the contained in the applet below the text).
To learn the answer, view this video.