What are your favorite brain teasers?

[Lakai]

I love these things. So in an attempt to gather as much of these puzzles/riddles as I can, I now create this thread.

Post all the answers in spoiler boxes within the same post.

I don’t know if this works online, but it should work in real life:

Ask someone to spell shop. Then ask them what they do when they see a green light.

SPOILER:

they should say stop instead of go

Here is the Roman numeral IX. Can you add one line or symbol to turn it into six?

SPOILER:

SIX

I like these becuase they are so simple that people can't guess them.

You guys know any more?

[Draelin]

You can also tell someone to spell "roast" (I usually make them spell several words--roast, most, post, coast), and then ask them what you put in a toaster. I especially liked using that one on a cousin ten years my junior who had just explained that he was way smarter than I could ever hope to be.

[Birdmonster]

There's this old classic I loved when I was ten...still gets people:

A rooster is sitting on top of a barn. It's sitting right at the apex of a triangular roof & lays an egg. Which was does it roll? Left or right?

SPOILER:

Roosters don't lay eggs. Stupid, eh?

[Bearflag70]

What does M-A-C-D-O-N-A-L-D spell?

MacDonald

What does M-A-C-N-E-I-L spell"

MacNeil

What does M-A-C-H-I-N-E spell?

MacHine

No, it spells machine, you moron!

[Birdmonster]

Alright, one more:
You're in a dark room with a candle, a wood stove and a gas lamp. You only have one match, so what do you light first?

SPOILER:

The match

[Anastasaeon]

Originally Posted by Birdmonster

There's this old classic I loved when I was ten...still gets people:

A rooster is sitting on top of a barn. It's sitting right at the apex of a triangular roof & lays an egg. Which was does it roll? Left or right?

SPOILER:

Roosters don't lay eggs. Stupid, eh?

This was actually a question on an "IQ test" some of us had to take at the factory I used to work for. (A handful of us were chosen to operate a couple of multimillion dollar computerised robotic machines - that sounds way cooler than it actually was. We had to pass the test first.) The test was full of questions similar to this: A man walked into a bar, and was immediately knocked out. Why? or: In a field you find two lumps of coal and carrot. How did they get there?
Along with the standard questions like CHAIN is to INGOT as KOYMNCIH GULE is to ? (I pulled this one off the internet because I couldn't remember the original question from the test, but it was very similar, and solved in the same manner.)

My favourite is my favourite only because of a discussion that took place after the test. One of our forklift drivers was repeating one of the riddles from the test to a friend: "Walking through the desert, you find a man lying dead with a backpack on. There are no footprints leading to him or from him. How did he get there?" The friend sat down and seriously began pondering this, furrowing her brow, and humming... really turning those gears. The driver glanced at me and asks if I know the answer. "He jumped from a plane and his parachute didn't open," I replied. The driver nodded at me. My friend hadn't heard my answer, and was still turning this over slowly in her mind. Finally, she gasps. She has the answer!
"It was a genie!" she said, triumphantly. The driver and I exchange a "where the heck did that come from?" look. Suddenly, my friend frowns. "No," she says. "No, that can't be right. How would he get that backpack in the bottle?" And goes back to seriously pondering the question again.

I love her half to death. That answer just made my day.

Oh, and spoilers to the above riddles:

SPOILER:

1. It was an iron bar he walked into.
2. That's what's left of a melted snowman.
3. CHAIN is to INGOT as KOYMNCIH GULE is to - QUESTION MARK. Count six letters above each letter. C=I, H=N, etc.

[Ghanima]

There's a man who loves animals and likes to keep them as pets. All of his pets are cats, except two. All of his pets are dogs, except two. And all his pets are rabbits, except two. How many pets does he have?

SPOILER:

Three

[Xema]

Originally Posted by Ghanima

There's a man who loves animals and likes to keep them as pets. All of his pets are cats, except two. All of his pets are dogs, except two. And all his pets are rabbits, except two. How many pets does he have?

How about this possible answer:

SPOILER:

Two: an alligator and a boa constrictorl

[Sublight]

Two boys are born on the same day of the same year to the same mother and father, but they are not twins. How is this possible?

SPOILER:

They're two of a set of triplets (or quadruplets, etc.)

A pet shop owner tells a customer, "this parrot is incredible. He'll repeat anything he hears." The customer buys the parrot and takes him home. The next day, he comes back to complain, saying "I talked to this parrot all day and he hasn't said a thing! I want my money back." The shopkeeper refuses, insisting he told the customer the truth. How could he?

SPOILER:

Several possible answers for this one.
a) The parrot is deaf, and doesn't hear anything.
b) The parrot will repeat what it hears, but not right then. Maybe later.
etc.

[Sublight]

A math one I just remembered:

Two mathematicians meet on the street. The first one says, "I haven't seen you in years, how are you?"
The second replies, "Very good, I'm married now and have three kids."
The first asks, "How old are they?"
The second says, "The product of their ages is 72, and the sum is the same as the number of windows in that building over there."
The first thinks for a moment and says, "Sorry, I can't figure out the answer."
The second then says "The oldest one has red hair."
The first mathematician then knows the answer immediately.

How old are the kids?

SPOILER:

8, 3 and 3. There are two sets of factors of 72 that add up to the same sum. Since the mathematician can't figure out the answer with the information given, it must be one of these two (8,3,3 and 2,6,6). Since the second mathematician mentions "the oldest one", the first knows that the twins must be the younger children.

[Cunctator]

One from an IQ test:

A man is standing at a spot on the earth's surface. It is not the North Pole. He walks one kilometre south, then one kilometre east, then one kilometre north. He ends up at the same spot where he was originally standing.

Where was the man originally standing?

SPOILER:

Draw a circle centred on the South Pole, with radius (2pi)^-1 kilometres. The man was originally standing at a point one kilometre north of any point on the circle.