With more than 150 million copies sold in 40 languages, Guinness World Records is one of the best-selling books in history.

In it, you'll find the shortest, tallest and fastest, alongside jaw-dropping human feats and eighth grade bathroom humor.

Some achievements are so over the top, it was hard to keep a straight face during interviews for this story.

But behind the spectacle is a meticulous system of British auditing – so strict it has crushed many more record attempts than it has certified. Even if what you see defies belief, you can trust that if it made it into the book it is real and as Guinness World Records declares, officially amazing.

Cecilia Vega: How are you feeling?

Colin Caplan: I'm feeling pumped.

Cecilia Vega: Yeah?

Colin Caplan: Yeah.

For Colin Caplan the stakes couldn't be higher.

After a year of planning, he's about to find out if his city — New Haven, Connecticut — can eat its way into history by hosting the world's largest pizza party.

Caplan, a local historian and food tour guide, is so obsessed with pizza, last year he chartered a jet to Washington and got his congresswoman to declare New Haven the pizza capital of America. 

Cecilia Vega: Is this a serious endeavor?

Colin Caplan: Yeah. Yeah. Yeah, I think it is. I'll tell you what. It-- it seems light and fun. But it's-- it's serious in a sense of what's on the line. 

What's on the line is the glory of a Guinness World Record. And people will do just about anything to get one.

Craig Glenday: Humans are such an interesting bunch, aren't we? And record breaking is an innately human thing. And if that means you do strange things like swallowing sausages whole, or-- climbing Everest, or running a marathon with a milk bottle on your head, then that's-- that's fine. That's great. 

Craig Glenday has been the book's editor-in-chief for the past 21 years. 

In his signature Scottish accent, he recounts with a straight face what is often a circus of absurdity.

Craig Glenday: You know, we get things like Fastest Time to Run Around my Garden Playing the Banjo with a Snake on my Head. It's like, "Next." They get a nice letter of r-- like, "Thank you but no thank you." 

Cutest babies and cutest dogs don't make the cut either. Records must meet strict criteria – they have to be filmed from multiple angles, verified by independent eyewitnesses, and measured with precision. 

Each year, Guinness World Records receives roughly 50,000 applications – but as many as 95% get rejected. The largest number of submissions come from the United States. 

Craig Glenday: One of my favorite days in the job was, I was at the X Games at the Staples Centre in LA and a dog zipped past me on a skateboard. And despite the heat, I chased after this dog and I found the owner and said, "I've never seen a dog on a skateboard." He said, "oh, this is Tillman, he loves skateboarding." I had a tape measure. We measured out 100 metres of the car park at the Staples center, and we set the record there and then, because I was so amazed by it. 

Cecilia Vega: Do you just walk through the world with a tape measure in your pocket?

Craig Glenday: Well, I do usually.

Cecilia Vega: Do you?

Craig Glenday: Yeah, I have a tape measure and a stopwatch. Because you never know.

Many of the record holders you know: Usain Bolt, for the fastest 200-meters, Beyonce, for the most Grammys.

And many you probably never even imagined.

Like serial record breaker David Rush: an Idaho tech worker who has broken more than 350 records and counting, including most bites taken from three apples while juggling for a minute, and most T-shirts worn during a half marathon.

And Monsieur Mangetout, that's Mr. Eats Everything in French. He held the record for the world's strangest diet. 

Craig Glenday: The guy who'd, you know, he'd supposedly eat in a Cessna because he could eat metal and glass.

Cecilia Vega: A Cessna plane?

Craig Glenday: Well, apparently it took him two years. We couldn't quite –

Cecilia Vega: Doesn't sound very healthy.

Craig Glenday: Well, I mean, he – his wife wouldn't let him use the toilet at home because if he'd been eating metal, it tends to come out like bullets and it would chip the porcelain. So he'd have to use a hotel with metal toilets near his house.

Cecilia Vega: This is the craziest interview I've ever done. I just say.

Craig Glenday: Sorry.

Cecilia Vega: I'm sorry. Come back to what you were saying, that when you-- 

Craig Glenday: I mean, for me, it's every day. So I don't quite get it, but yeah. OK.

Cecilia Vega: (sighs)

Craig Glenday: He could do glass and metal. But he couldn't do chains. But to meet him was a real honor for me because he was like a childhood hero for me. 

Cecilia Vega: You must get this question all the time. Why?

Craig Glenday: Why? I mean, it's different for everyone. Everyone has a different reason. Some just want fame, some want to be in print. We do validate people that do things that others might seem a bit weird, like eating aircraft and stuff.

Cecilia Vega: Do you not see that as weird?

Craig Glenday: I mean, I see it as really interesting.

Cecilia Vega: I gotta tell you, I thought it would be a little crazier in here.

Inside the company's London headquarters, Glenday keeps a cabinet of greatest hits.

Craig Glenday: It's Craig's Cabinet of Curioddities.

Like the world's smallest playing cards, and a giant size 29 shoe.

Cecilia Vega: I'm like the Vanna White of oddities here. What is this?

Craig Glenday: If you have a little investigation of that, it's the world's oldest vomit.

Cecilia Vega: Vomit. You got me on that one.

Craig Glenday: --106-- it doesn't smell. And it's obviously petrified

Not everyone chooses to break records.

Cecilia Vega: I'm 5'10", so what was she?

Craig Glenday: She's just on 7'.

The tallest and shortest people often have had genetic conditions.

The woman with the longest finger nails – 43 feet – hasn't cut them since her daughter, who painted her nails, passed away in 1997.

Cecilia Vega: So she still holds the record?

Craig Glenday: Still has the record. And I think that's the longest ever measured.

The idea for the book began during a hunting trip at this country estate in Ireland, where the manager of the Guinness brewery got into an argument over who could name the fastest game bird in Europe. 

To settle future pub debates, he commissioned a book of superlatives which eventually became the Guinness World Records. The first one was published in 1955.

Craig Glenday: The initial reaction from the book trade was not that positive. In the first sales meeting ever, the-- the salesperson wrote "six" on the slip. And they said, "W-- do you mean 6,000? 600?" Said, "No. Six."

Cecilia Vega: They just wanted six?

Craig Glenday: Six for the whole country.

Cecilia Vega: Copies?

Craig Glenday: Yeah. By the end of the week it was, like, 10,000.

Cecilia Vega: They sold that quickly.

Craig Glenday: It just blew up.

Seventy years later, it's still a hit at school book fairs, but today the name Guinness World Records is synonymous with viral stunts that become click bait gold. 

Cecilia Vega: Is Google your biggest competition? I could pull my phone out right now and search the world's fastest bird.

Craig Glenday: You might as well open the window and shout your question into the street. And you'll get an answer, yeah, but is it the right one? Well, I can say itI know Sultan Kösen's 8'3" because I've-- I was there with a tape measure. I measured him. 

He's also measured the shortest person – who he learned about after a woodcutter passed through a remote village in Nepal and alerted the team at Guinness World Records. 

Craig Glenday: So there was confidence enough for me to then go to Nepal and--

Cecilia Vega: You get on a flight and go--

Craig Glenday: And I-- to find him.

Cecilia Vega: --to Nepal to measure this person?

Craig Glenday: Yeah, yeah. And we would never have known about him had that woodcutter not gone through the village that day and sent us the video footage.

And then there are the rules: so rigid, they've sparked office debates over who makes the cut for the largest gathering of people dressed as Smurfs.

Craig Glenday: So. It's like, OK, well, what is this Smurf? What do they wear? Do they all have blue skin? Yes.you know you might have to write guidelines for any possible topic. So we've got this huge big book of experts, you know from archaeologists to –

Cecilia Vega: Smurfs.

Craig Glenday: – to Smurfologists. You know like, we've got a myrmecologist, which.

Cecilia Vega: What is that?

Craig Glenday: Myrmecologist, an ant expert. If we've got a question about what's the most dangerous ant

Cecilia Vega: Quick, get the myrmecologist on line 9.

Craig Glenday: Yeah, so you get, of like, we've just found this big ant. Is it the biggest?

For large events like the New Haven pizza party, Guinness World Records sometimes sends an adjudicator responsible for enforcing the rules from headquarters.

Thomas Bradford is one of 81 adjudicators the company employs across six continents.

His day job is as a performer at Disney. But when it's go time, he puts on his trademark blue jacket. 

Thomas Bradford: The largest gathering of people dressed as dinosaurs was one of my favorite events. You kind of expect people to just come in the classic, you know, inflatable T-Rex costume. But we saw--

Cecilia Vega: What-- what do they come in?

Thomas Bradford: --Diplodocus, Triceratop-- like, you name it, we had it.

Cecilia Vega: Legit gear?

Thomas Bradford: Everything. I had to turn away people that were dressed as Godzilla, 'cause Godzilla is not a dinosaur.

Cecilia Vega: How do you break it to a dinosaur in a bad costume that they don't qualify?

Thomas Bradford: You kinda just have to play the role. I think my accent helps. And there is a level of, you know, authority that comes with a British accent--

Cecilia Vega: School principal.

Thomas Bradford: Very much that.

Thomas Bradford: The largest pizza party is probably the most competitive record that I've ever been a part of.

Cecilia Vega: Is that true?

Thomas Bradford: I didn't think it would be as-- it's-- it's a lot. Yeah, so--

Cecilia Vega: Been stressin' you out?

Thomas Bradford: It's-- this is probably one of the most stressful record attempts I've had. 

Colin Caplan needs 3,358 people to show up in order to beat the current record.

Cecilia Vega: You want to beat Tulsa?

Colin Caplan: We're gonna beat Tulsa, Oklahoma.

Participants get 15 minutes to eat two slices of pizza and drink a bottle of water. But here's the catch: they have to stay until the party is officially over and…

Thomas Bradford: They must eat the entire pizza, no one can leave their crusts. They have to eat the crust.

Cecilia Vega: What makes a pizza party like this so difficult?

Thomas Bradford: People It's you know, You don't know if they're gonna stay for 15 minutes. They might wait for 14 and be like, "I'm fine." You're disqualified if you leave after 14 minutes, you know? So that's-- the people is the-- the toughest thing.

At first, it was slow going. But then, in came the pizza obsessed: college students, children, those in their finest pepperoni attire.

Colin Caplan: It's 10,000 slices, which is 625 pizzas in about three-and-a-half hours.

Caplan's pursuit of a record didn't come cheap — brands and businesses chasing titles for marketing must pay fees. He said he paid nearly $30,000 and fundraised six figures to cover all the costs, including eight ovens and all that cheese.

When Thomas Bradford wasn't busy being a celebrity, he and a group of 100 volunteers kept the tally.

With an hour to go, Caplan was still trying to make the pie calculations add up.

Colin Caplan: We can actually feed 1,800 people starting at 6:00 still. And that means that we could 100% beat the record and almost get to 5,000.

So did they? Finally, the verdict: 4,525 people gathered for a new Guinness World Record, and a slice of history.

Craig Glenday: Human beings are nearly the same everywhere they are really, because they're trying to get through from birth to death and have as much fun and enjoy life and get all the experiences that you can. And we see this every day. The world is full of these amazing fun things if you just look in the right place. 

Produced by Ayesha Siddiqi. Associate producer, Kit Ramgopal. Broadcast associate, Katie Jahns. News associate, Ava Peabody. Edited by Mike Levine.