If you thought the T-Rex looked scary on screen, apparently things weren’t all that different during filming either. Thanks to the rain, the animatronic T-Rex would frequently short circuit and ‘come alive’ of its own accord. Producer Kathleen Kennedy has said: “We’d be, like, eating lunch, and all of a sudden a T-Rex would come alive. At first we didn’t know what was happening, and then we realized it was the rain. You’d hear people start screaming.”

Alan and Ellie have a sign that says “No animal released without paperwork completely filled out” hanging in their trailer.

The noise used to convey the velociraptors talking to each other is actually the sound of tortoises having sex. Rydstrom spent months recording animal noises. Rydstrom’s work on Jurassic Park ended up winning him two Academy Awards.

Sam Neill injured himself with the flare he uses to distract the T. rex. According to Neill, “It dropped some burning phosphorous on me and got under my watch and took a chunk of my arm out.”

The screams in this scene are genuine — the animatronic T. rex was not supposed to break the plexiglass.

The new sequel, Jurassic World , very nearly ended up as a very different film. Before production was dropped and the idea shelved many years ago, a script was written for Jurassic Park 4 that involved genetically altered dinosaurs being bred for war and trained to carry weapons for battle.

Why exactly was that Triceratops so ill? Michael Crichton’s novel supplies an answer. It is explained that the dino lacks suitable teeth for chewing and so, like birds, would swallow rocks and use them to grind food in its digestive tract. After six weeks, the rocks would become too smooth to be useful, and the animal would regurgitate them. When finding new rocks to use, the Triceratops also swallowed toxic berries.

One of the scariest dinosaurs seen in the first film is the all-frills, all-spills Dilophosaurus. And yet, it’s most memorable features were all made up one way or the other. Michael Crichton, author of the original novel, invented the dino’s deadly venom-spitting ability, and Spielberg added the terrifying rattling neck-frill. In real life, the Dilophosaurus didn’t have either of these traits. And yet everyone who grew up watching the film now thinks differently.

Jaws is playing on one of Nedry’s computer screens.

It’s no coincidence that Ian Malcolm wears black throughout most of the film, while Hammond wears mostly white. This is to represent the fact that the two are diametrically opposed idealistically.

People have asked if dinosaur DNA could really be cloned. If there is a way, we do not yet have the technology. If you took petrified DNA it would still be too degraded. And there is no equivalent to a dinosaur egg in which to incubate the embryos. The paleontologist, Jack Horner, who was a consultant on the film, said he thought it might be possible to genetically modify a chicken embryo to activate dormant genes for dinosaur-like traits. Even if that happened it would still not be a clone of a dinosaur.

The idea to have Mr. DNA explain the science behind Jurassic Park was a fluke. “I remember Steven [Spielberg] and I were wrestling with that very issue, about the DNA, and one of us said, ‘What are we supposed to do? Have a little animated character called Mr. DNA?’ And the other one said, ‘Yes! That’s exactly what we’re going to do!’”

The velociraptors costumes were done Godzilla-style, equipped with puppeteers in lizard suits. The man-sized velociraptors were much bigger than the real species, though shortly before the movie’s release, paleontologists discovered a larger related species, the Utahraptor. Winston joked, “We made it, then they discovered it.”

Juliette Binoche and Robin Wright were first offered the role of Dr. Ellie Sattler, which would end up going to Laura Dern. Jodie Foster, Joan Cusack, Julia Roberts, Linda Hamilton, Sandra Bullock, Julianne Moore and Sarah Jessica Parkert all tested for the role.

In the dining room we see corporate slides that suggest Hammond anticipated Jurassic Park becoming more popular than both “sports” and “zoos.”

Spielberg famously lured acclaimed British director Sir Richard Attenborough out of a 14-year acting retirement and cast him as John Hammond. But Jurassic Park was actually the third film Spielberg had asked him to appear in.

Originally, Jurassic Park was going to end just with Grant saving the kids from the raptors. He was going to shoot one dead and then use a mechanical T-Rex skeleton in the foyer to kill the other. However, Spielberg realised that he needed one last triumphant return for the T-Rex and so changed the ending to include him in. Maybe this late change explains the long-debated question of how the T-Rex seems to appear out of nowhere?

Universal released a 3D version of “Jurassic Park” in theaters. The conversion from 2D cost $10 million, and it earned the 20-year-old film another $45.4 million in domestic ticket sales.

A lot of work went into creating dinosaurs that were life-like. After all of that work, they got about 15 minutes of time on the big screen. Considering the movie was 127 minutes long, that is not a whole lot of time.

The T-Rex was a combination of an elephant trumpeting and, hilariously, penguin mating sounds, as well as dog, tiger and alligator noises.

Jurassic Park earned a whopping $357 million in North America and a total of $914 million worldwide. That was enough to surpass Spielberg’s E.T. to take the record as the biggest hit movie of all time, a record it held for nearly five years, until Titanic.

Both William Hurt and Harrison Ford were offered the role of Dr. Alan Grant, which Sam Neill would eventually land. Richard Dreyfuss was also considered.

The iconic rippling water scene was inspired by the mirror shaking in Spielberg’s car while he was listening to Earth, Wind, and Fire. The effect was created by placing the glass of water on a vibrating guitar.

In the final scene, the Jurassic Park logo on the jeep is covered in mud and spells out “UR ASS PARK,” a subtle joke that “you’re lucky to get out with your ass in one piece.”

Phil Tippett really sucked at his job.