- Come on. - All right, that was an easy one.

All right, balloon in the cup.

- Oh, no. - What?

- You didn't do that. - What are you doing?

- I'm never going to look at anyone's pictures of their room the same anymore. - I'll tell you.

My assumptions, they were wrong.

Guys, today we're talking about optical illusions.

And I know you think my eyes are huge but they're just normal.

What?

You might remember a few weeks ago, we started the show off with the OK Go video, the new one that is filled with optical illusions.

It took over three weeks to put together. It is a beautiful thing.

That's what we're talking about today: all about optical illusions, things that look one way but are actually another.

Who said that?

Who did?

We don't know.

That was a video called "Assumptions" from a channel called Quirkology. It got over 5 million views because nothing in that video...

...is as it seems.

Ladies and gentlemen, the Hyper-matrix.

- Look at that. That is— - It's wave in a wall.

What is happening?

What is happening?

And the reason it says Hyundai Motor Group is because this is part of an art installation called Hyper-matrix.

And it's at the Hyundai Motor Group pavilion in Korea, and this comes from a Seoul based artist that the group has called jonpasang.

But there are thousands of motors behind 300 by 300 millimeter cubes that are going in and out.

The cubes are moving with the sounds, but there's also projection mapping on top of the cubes, which makes this full immersive experience like this, like we're seeing right here.

- That is not a real guy. - That's a Hadouken.

Hadouken.

We're talking optical illusions. - Yup.

This is a really freaky one. It'll make you feel like you're hallucinating.

If you have any kind of epilepsy or sensitivity to flashing lights, do not watch this.

- T... L... - No, you don't say the letters.

O... F...

You can look away now.

No.

Don't look at me. Don't look at me.

You look fine.

That video is from the Science Forum channel.

This is obviously a popular video, because it's got almost 13 million views.

That made things wavy, like everything was a heat wave.

It's created when your brain cells that are detecting motion just get fatigued.

So after your eyes look away, the cells that are detecting the motion in the other direction are more active.

You sound like the substitute teacher in physics class that got stuck explaining the hardest thing there is to explain.

When I'm like a gym teacher.

You know, like there's some cells.

And they're going to go over here.

OK, Miles. We are going to watch the style of dance that is called sock trousers dance, or strumpfhosentanz if you're saying it in its native tongue.

- Oh, "strumpfrozenhands," yeah. - Beautiful.

Actually, it's "strufrozentonsils."

See?

Wait. Wait, wait, wait, wait.

- It looks like the biggest conjoined twin ever. - It looks horrifying.

- Your brain so badly wants to connect the right arms and legs to the right torso. - But it doesn't work, and then you end up—

Just confused.

4.5 million views on this. That means that 4.5 million other brains have also failed to connect the right body parts and the right—

Yeah.

Earnest, did you ever play with sidewalk chalk when you were growing up?

Of course I did.

This guy, Edgar Mueller, takes sidewalk chalk to a whole thousand new levels.

I like the people who are like posing on the side.

That's absolutely what I would be doing.

This particular artist's name is Edgar Mueller. He's sort of very well known for his 3D sidewalk art.

This particular piece was commissioned as part of the Festival of World Culture that took place in Dublin, Ireland in August, of 2008.

Since 1998, he has held the title of Maestro Madonnari, which is Master Street Painter, which is a title I didn't even know existed.

OK, what you're going to see is completely real.

There's no Hollywood magic. There's no computer wizardry, no wizard computery.

What do we have here? Just a couple of slopes.

Wait, but they just did that in reverse, right?

I said no Hollywood magic.

What sorcery is this!?

This was made by Koukichi Sugihara.

Your brain likes to take shortcuts, so it sees this, and it thinks that it knows what it's looking at.

- Yeah. - And it fills in the gaps for you.

It was the winner of the Illusion of the Year in 2010.

Sugihara-san, you are the best.

I know this is an optical illusion show, but sometimes what you see can mess with what you hear.

We did feature this before on the show recently.

Listen to Greg speaking.

- Bar. Bar. Bar. - Bar. Bar.

If you heard bar bar bar, you'd be right. How about now?

Bar. Bar. Bar.

Chances are, you heard far far far this time, except you didn't.

This is a perfect example of something called the McGurk effect, which shows how our visuals can alter what we believe we're hearing.

I'll play two tones, and you tell me if they're ascending or descending.

High, low.

Low, high.

If you compare with enough people, you'll all have different answers.

It's an auditory illusion called the Tritone paradox.

It's created in such a way that the tones contain both a higher and lower frequency in them, but our brains have a preference of which to listen to.

- Oh. - Hm.

- So our brains are different. - Yeah.

We have different brains.

What this episode taught me is that our brains are stupid.

Get with it, brain! Stop being so tricked.

What, you're going to let your eyes tell you what to do?

So those are some of our favorite illusions. Let us know some of your favorites in the comments.

We have some more optical illusions coming up for you after the show, so stick around. Check those out.

Now play us out, Young Rival.

Literally, I don't see anything.

You see nothing?

I see it! I see it!

There you go. You got it.

Now I'm locked into this.

The end. It says the end.

Now you can see it. So now you can—

I feel like now I'm scared to move my eyes back to normal.