This is simple – in hindsight – yet so convincing. If you want to challenge yourself, stop before 25-28 seconds are up and try figuring it out. There is a pause after the four balls are added at this time, before they give the game away.
When you see it shown the second time (55 seconds into the video) it still works. For me, anyway.
I’m blatantly flogging this from Carl Zimmer who flogged it from Koukichi Sugihara. I know, I know, but it’s too good to pass up. Especially when you’re short on time. I hope they can forgive me for falling for temptation…
If you don’t know Carl Zimmer’s writing and popular science is your thing, do read his blog. It’s one of the better ones around. Of his recent posts, Skull Caps and Genomes looks intriguing. (It’ll have to wait until I have time, unfortunately…)
A sample of lighter posts from Code for life: