Is It True That T. Rex Could Only See Things That Were Moving?

Freer Law/iStock via Getty Images
Freer Law/iStock via Getty Images

I rewatched Jurassic Park a few weeks ago and, from the story to the special effects, it still holds up. But I’ve been nagged by one thing that’s stuck with me from the first time I saw the movie—a thing that has been ingrained in our collective knowledge and perception of dinosaurs: protagonist Alan Grant's assertion about what the Tyrannosaurus rex can and can’t see.

In the scene where the T. rex gets loose and attacks a group of human characters, Grant says to Lex, “Don’t move. It can’t see us if we don’t move.” Sure enough, the dinosaur gets up in their faces without noticing them right after he says that. For what it's worth, Michael Crichton does explain in the Jurassic Park novel that the amphibian DNA used to help bring the dinosaurs to life hobbled their visual cortices. Director Steven Spielberg and the movie's screenwriters dropped the ball big time here, importing the dinosaurs’ vision problems but not the explanation for them. Instead, in the movie, Grant comes off like he’s stating an accepted dino fact.

Sci-Fi versus Reality

He’s not. In the last few years, real-world paleontologists have proven Dr. Grant very wrong. In 2006, Kent Stevens from the University of Oregon did an experiment inspired by that very scene to figure out what sort of binocular range (the field of view both eyes can see simultaneously) T. rex might have had. The wider that range, the better an animal’s depth perception and capacity to distinguish objects that are motionless or camouflaged.

Stevens built a scale model of the T. rex’s head and popped in some taxidermic eyes based on the eyes of three animals pretty closely related to T. rex—alligators, ostriches, and eagles—and adapted for situations that a dinosaur would have likely encountered. As he explains on his website, he used a technique called “inverse perimetry” to estimate “whether a given probe would be visible, based on whether there is a clear, unobstructed view of the pupil along a line of sight,” and mapped the model’s field of view.

Stevens' model study suggests that T. rex had a binocular range of around 55°, better than that of modern-day hawks and eagles. And it would have only gotten better. Paleontologists know from the fossil record that, over millennia, T. rex’s eyes got larger and its snout got lower and narrower, giving it even clearer sight lines than Stevens’ model.

For more on dino-vision, see Stevens' web page and the study. For more on other JP mistakes that make dino geeks fume, see this Wikipedia list.

What's the Difference Between Cement and Concrete?

Vladimir Kokorin/iStock via Getty Images
Vladimir Kokorin/iStock via Getty Images

Picture yourself walking down a city block. The sidewalk you follow may be obscured by shuffling feet and discarded gum, but it’s clearly made from something hard, smooth, and gray. What may be less clear is the proper name for that material: Is it concrete or cement? Is there even a real difference between the two words?

Though they’re often used interchangeably, concrete and cement describe different yet related elements of the blocks, flooring, and walls that make up many everyday structures. In simple terms, concrete is the name of the gray, gritty building material used in construction, and cement is an ingredient used in concrete.

Cement is a dry powder mixture that looks much different from the wet stuff poured out of so-called cement trucks. It’s made from minerals that have been crushed up and mixed together. Exactly what kind of minerals it’s made from varies: Limestone and clay are commonly used today, but anything from seashells to volcanic ash is suitable. After the ingredients are mixed together the first time, they’re fired in a kiln at 2642°F to form strong new compounds, then cooled, crushed, and combined again.

Cement
Cement
lior2/iStock via Getty Images

This mixture is useless on its own. Before it’s ready to be used in construction projects, the cement must be mixed with water and an aggregate, such as sand, to form a moldable paste. This substance is known as concrete. It fills whatever mold it’s poured into and quickly hardens into a solid, rock-like form, which is partly why it’s become the most widely-used building material on Earth.

So whether you’re etching your initials into a wet sidewalk slab, power-hosing your back patio, or admiring some Brutalist architecture, you’re dealing with concrete. But if you ever happen to be handling a chalky gray powder that hasn’t been mixed with water, cement is the correct label to use.

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Why Do You Stop Feeling Tired As Soon As You Climb Into Bed?

tommaso79/iStock via Getty Images
tommaso79/iStock via Getty Images

There are few situations more frustrating: After a day spent nodding off at your desk, on the train, and on your couch, you suddenly can't sleep the moment you crawl into bed. It's not that you aren't tired or have insomnia, necessarily. Like a curse designed just to torture you, the sleeplessness only seems to occur when you're in your own bed at home, a.k.a. the place where you'd prefer to do your sleeping.

This maddening problem isn't in your head. According to TIME, many people have more trouble falling asleep in their own beds than they do elsewhere thanks to a phenomenon called learned or conditioned arousal. Conditioned arousal develops when you inadvertently train your body to associate your bed with being awake. In many cases, this results from doing stimulating activities in bed. For instance: If you like to slip under the covers and spend 40 minutes watching Netflix before closing your eyes, you're teaching your brain that your bed isn't for sleeping. That means the next time your head hits the pillow, your body will respond by preparing for the next episode of Friends instead of releasing the chemicals that help you fall asleep. The same goes for scrolling through apps, eating, and even reading in bed.

Doing things that aren't sleeping in bed isn't the only way to develop conditioned arousal. If there are other factors keeping you up at night—like thoughts about your day, or that cup of coffee you had at 8 p.m.—they can lead to the same result. Your brain starts to associate being in bed with tossing and turning all night, so even if those mental and physical stimulants go away, the muscle memory of being awake in bed remains.

Conditioned arousal is a vicious cycle that can't be broken in one night. The only way to manage it, according to the American Psychological Association (APA), is to minimize behaviors that contribute to poor sleep habits and to reserve your bed for sleeping (though sex is OK, according to the APA).

If you're a nighttime scroller, browse apps in a different room before getting into bed, or skip checking your phone at the end of the day altogether. When you spend more than 20 minutes struggling to fall asleep in bed, get up and move to a different part of the house until you get sleepy again; this will stop your brain from strengthening the association between your bed and feeling restless. The results won't be instant, but by sticking to a new sleep routine, you should eventually train your body to follow healthier patterns.

Of course, combating conditioned arousal alone isn't always effective. In people with conditions like anxiety and insomnia, intrusive thoughts and genetic factors can prevent them from falling asleep even under ideal circumstances. In such cases, the help of a medical professional may be required to sleep more soundly.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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