10 best internet puzzles, optical illusions and brainteasers to exercise your mind

The internet is forever offering up news ways for us lose our minds. Whether it's a picture of a dress or a puzzle with an answer no one can agree on, there appears to be no better way of sinking work hours than a good, old-fashioned brainteaser.

These days it seems we can barely go a week without another "viral phenomenon" sweeping the 'net and causing it to go into overdrive. While their use beyond being great procrastination material is limited, brainteasers and illusions can occasionally provide insight into the human mind's more intricate and mysterious workings.

With that in mind, here are some of our favourite illusions and brain-ticklers from around the web that will leave you amused, confused or just plain despairing.

Hearts

What colour are the hearts in the box? Purple and orange, right? Wrong. Actually, all the hearts are exactly the same shade of pink. The reason they look different is because of how the green and blue stripes alternate as they run through them, combined with how the human mind perceives an object's colour based on the colours surrounding it. Don't believe us? Check out this YouTube video and see for yourself.

Ball through a mirror

This video of a young man appearing to throw a ball to himself through a mirror has notched up more than 5.4 million loops on Vine since being uploaded this April. Uploader Kevin Parry describes himself as a stop-motion animator, which gives us some idea as to how the seemingly amazing feat was been pulled off (hint: video editing). Still, it's pretty damned clever.

The jelly bean problem

The basic premise behind the jelly bean problem is this: you have to choose between a green, a blue and a red jelly bean. Two of them are poisonous and will kill you if eaten. You chose the green one, but before you eat it, somebody tells you that they are going to remove a poisonous jelly bean and take away a blue one. You're allowed one last chance to change your mind. Do you pick the remaining red jelly bean or the green one you have in your hand?

If you stuck with green, you're now dead. Tim Urban of Wait But Why explains: "When you initially picked the green jelly bean, there was a 1/3 chance that it was the safe one to eat, and a 2/3 chance that it was poisonous and the safe one was still on the stump. When the man removed a poisonous blue jelly bean from the stump, it told you no new info about the green jelly bean in your hand − that still had a 1/3 chance of being safe.

"But removing the blue jelly bean told you a lot about the red jelly bean − it told you that if the safe jelly bean had been on the stump, the red one is safe.

"Put another way, if you picked a poisonous jelly bean, which you would do two-thirds of the time, then choosing to switch after he removes one will save you every time. If you picked the safe one to start off with, which happens one-third of the time, then switching will kill you. So switching is a good choice two-thirds of the time."

Brain hurting yet? Good. Let's move on.

The Fraser spiral

Named not after our favourite TV psychiatrist but British psychologist Sir James Fraser, this optical illusion features a trippy spiral.

Or is it a spiral? What you're actually looking at here is a series of concentric circles, which your mind is tricked into thinking is a spiral because of the arc segments overlapping it. Don't believe us? Place your cursor at the uppermost part of an outer line and follow it around. You'll quickly find yourself back at your starting point.

The bus

This brainteaser appeared on National Geographic's Brain Games television show and, despite the fact it's aimed at children, has managed to leave adults puzzled too. The challenge is to figure out which way the bus is travelling. We'll give you a hint: the answer will be different for UK and US readers.

Still can't figure it out? Scroll to the end for the answer*.

How many threes?

This one appears simple enough – just count how many threes you see in the image. Most people seem to agree on between 15 and 19, although others count as many as 28. What do you think?

The train track illusion

This example of the so-called Jastrow Illusion – named after its discovery by psychologist Joseph Jastrow in the late 19th century – was spotted in a child's train track set by BBC's Marc Blank-Settle. At first glance it appears the two wooden track pieces are different sizes, until one is place on top of the other and....hold on, what?

The illusion occurs because of the way the two pieces are positioned − with the longer side of the bottom piece contrasting with shorter side of the top piece − combined with the viewing angle of camera itself. That's the official excuse anyway – we're going with either black magic, aliens or the Illuminati.

The fruit puzzle

This puzzle is based around a mathematics equation using apples, bananas and coconuts in the place of numbers and tasks you with working out the value of a sum based on the picture. While it may appear pretty straightforward to some, internet users continue to debate over the answer.

As it turns out, this puzzle requires a sharp eye as well as a bit of arithmetic. ** Scroll to the bottom for the answer.

The silhouette

This painting has left thousands of internet users stumped after being published by Facebook user Savannah Root on 12 April. The post has since notched up more than 31,000 views and has been shared nearly 6,000 times, challenging users to decipher the hidden image. Some have been able to spot it instantly, although others don't seem to be having such an easy time of it. Can't make it out? Scroll to the end for the answer***.

The red dot test

Take a look at the picture below. See anything other than a red dot? Some people can't see anything, whereas others will see the outline of a horse. Those with keener eyesight might even be able to pick out grass and a saddle. Don't believe us? Flip the image to reveal all.

*The key to solving the puzzle is figuring out where the passenger doors would be. If you're in the UK, the bus would travelling to the right because we drive on the left-hand side of the road. However in the US, where people drive on the right side of the road, the bus would be travelling to the left.

** The answer is 14

***It's a cowboy