Now this is interesting.

And in that situation, if this guy screamed green then that means that if this guy saw an odd number of green hats from here on down, and one of these guys behind him, or every time someone behind you says green after that, then the number of green hats that are odd or even in front of that person will change.

So that guy uses that same logic to say OK, there must be three green hats from me on down.

Now this guy's turn.

Without any other information, we assume that there's a 50 50 chance that the hat on the top of your head is a purple or a green one.

Now this guy, he counts the number of green hats in front of him.

So count the green.

And so I went home, and I made a prototype of this hat.

And so he counts.

I've always admired that hat.

Whoever's in the back has to do this, right?

The cap?

The woman tried on one hat after another, then left the hat shop.

My hat.

My hats!

The hat?

You don't like my hat? Why?

So he also sees an odd number of green hats, so he knows that he must not have a green hat, because if he had a green hat, then it would turn the number of green hats that he saw into even.

He counts the green actually only.

Hey, look. The hat, he is a Frisbee.

One, two, three, four green hats.

So check.

What did you do with Alan's coat?

There's one, two, three, four, five.

Try a new hat on.

He obviously can't look at his own head, but he'll see everyone else's hats.

Now, this guy, he looks forward and he counts one, two, three, four, five green hats.

Because this guy didn't say green.

Check out that hat.

So they either get a mauve or a green hat on the back of your head.

The match is in that hat!

One hat.

You want my hat?

It's a giraffe.

It's this guy.

Is this your hat?

This car.

And they say, while the room is completely pitch dark, we're going to place a hat on each of your heads.

And I got to think. Do you have a hat or a scarf or something?

Put your hat on. Put your hat on.

I shall place the Sorting Hat on your head and you will be sorted into your houses.

He took off his cap in front of the entrance.

And so then they'll ask this guy, what color is the hat on your head?

If this guy counts the green hats of the eight people in front of him, and he says wow, there's only an even number of green hats, he could say, wow I must have a green hat.

You need the hat.