First, get the water boiling on the stove. Then, as simultaneously as possible, start both hourglasses and drop the egg in the pot.
When the 4-minute hourglass runs out, turn it over.
When the 7-minute timer runs out, turn it over.
At eight minutes, the 4-minute hourglass will run out again.
At this exact moment, turn the 7-minute timer over again. It’s only been running for a minute since its last flip, so it will only take one minute to empty again. When it does, the egg will have boiled for exactly nine minutes, and your master will have no cause for complaint.
29. Eye on the ball
As you will have seen at the end of the video, the ‘test’ is a bit of trick. It’s not about how many times the ball gets passed. It’s all about the gorilla.
Didn’t see it? Don’t worry: 50% of the people this video is shown to don’t notice the gorilla at all – a phenomenon called ‘inattentional blindness’. When you’re concentrating on a complex or difficult task, your brain simply does not see what you’re not attending to. (One good reason not to drive and talk on your cellphone at the same time!) You also may ‘tune in’ to particular qualities, like brightness, colour, movement or shape – in this case, the gorilla suit is black, and you’re focusing on the white shirts.
Inattentional blindness is used by stage magicians: they’ll focus the audience’s attention on the rabbit in one hand, for example, while working a trick with the other. In stage magic, this is called ‘misdirection’.
This video test, created by psychologists Daniel Simons and Christopher Chabris, has become quite famous. Read more about their work at The Invisible Gorilla.