The mind is an extraordinary tool, capable of such intense laser-focus, that it can exclude all other data, as is so beautifully demonstrated in this very short test of your attention.
If you’ve never watched this before, drop everything you’re doing and take one minute out of your life to perform the task (you don’t need the sound on – instructions are given on the screen and it’s a purely visual exercise).
Once you've watched it (you did watch it, didn't you?), or if you've seen it before and you already know the score, you can read on.
Spoilers below.
(Watch the video)