Boughs Of Folly: Science Blunders In National Lampoon’s ‘Christmas Vacation’

It’s that time of year, when the Griswold clan—led by its hapless patriarch, Clark—stumbles through a gauntlet of yuletide traps in National Lampoon’s Christmas Vacation. If you’re like me, you’ve seen this iconic holiday film at least two dozen times. You know every scene by heart, and yet you still laugh. It truly is the gift that keeps on giving, Clark.

But because I’m part of Science Friday, I can’t simply reminisce over Eddie’s fashionable dickie or Aunt Bethany’s creative Jell-O recipe. So I have attempted to bring a little scientific scrutiny to several of the more memorable scenes to see if they could happen in real life, or if there’s anything we can learn from them. To help me in this endeavor, I consulted a few good-natured folks with expertise in subjects like food science, health, engineering, and physics (some of whom you might recognize from the radio show).

I realize this movie is pure comedy, and picking it apart is perhaps disrespectful to its place in the Christmas movie pantheon. But c’mon, isn’t there also some fun in lampooning the master? Bingo.

THE CHRISTMAS TURKEY SCENE

During the family’s holiday feast, Clark calls everyone’s attention to the pièce de résistance: a perfectly browned turkey. “If this turkey tastes half as good as it looks, I think we’re all in for a very big treat,” he coos. But the moment Clark slices into its golden skin, the bird pops open with a puff of steam, revealing desiccated meat (plus the heart). What’s wrong with this picture?

“It would be impossible for the exterior to look so pristine and the interior to be all dried out,” says former SciFri guest Meathead Goldwyn, the founder of AmazingRibs.com. Meat cooks from the outside in, so “that exterior would shrink just like the interior—it would wrinkle, and it would get very, very dark.” In other words, the turkey “would have looked like a deflated football.”

That’s because turkey meat is about 75 percent water, and the entire bird gets smaller as water evaporates during cooking. How dehydrated it gets depends on how long you cook it, and at what temperature, says Meathead. “I think there’s this strong tendency of a lot of people [to] cook way too hot,” he says. For appetizing results, he recommends an oven temp of 325°F. “At that number, you get good, crispy skin, you render fat, and you don’t steam off too much moisture,” he says.

In the film, cousin-in-law Catherine laments that she and Clark’s wife, Ellen, “put it in too early.” In reality, the amount of time required to cook a turkey can take anywhere from 90 minutes to two-and-a-half hours, depending on the size of the bird, which reflects the thickness of the meat. “And if it’s a very, very thick breast, then it takes longer for the heat to work its way down from the outside to the inside,” says Meathead.

To avoid a Griswold turkastrophe, the best way to tell when your fowl is cooked is to stick a digital thermometer (as opposed to a pop-up thermometer) in the center of the breast for about five seconds to get a good read, advises Meathead. “Any recipe that says ‘cook for X amount of time’ is a recipe for disaster,” he says. “Always use a thermometer. Thermometer is the measure of doneness.” The USDA recommends that “done” turkey meat be 165°F, to ensure that bacteria are dead. Meathead suggests taking the bird out when the thermometer reads 160, because the heat energy stored up inside the turkey will continue cooking it (the phenomenon is called “carry over”) till it reaches 165°F. If you do that, he says, “you’ll have a juicy bird.” (See more of Meathead’s turkey tips here.)

THE ‘HER EYES ARE FROZEN’ SCENE

In this scene, Clark parades his family through a snowy woodland to find the perfect Christmas tree,* finally spotting it in a halo of light. His daughter, Audrey, can’t appreciate it, however. She’s visibly shivering from the cold, and as Ellen points out, “her eyes are frozen.”

Can eyes really freeze? Yes, parts can. This is actually something Christmas Vacation might have inadvertently gotten right, at least in theory.

For insight (sorry) on the matter, I consulted Scott McIntosh, an associate professor in the Division of Emergency Medicine at the University of Utah and author of the “Wilderness Medical Society Practice Guidelines for the Treatment and Prevention of Frostbite.”

The outermost layer of the cornea, called the corneal epithelium, is technically dead and “sheds constantly—like the skin,” McIntosh writes in an email. “But the deeper layers are alive and can freeze with the right conditions.”

Fortunately, we have a few methods of preventing this in the first place: “blinking (which keeps the eye warm) and keeping the eyelids closed (which prevents the cold from reaching the cornea).” McIntosh also advises wearing protective eyewear when the eye might be susceptible.

But if the deeper corneal layers do freeze—like this Iditarod Trail Sled Dog Race participant’s did—then treatment might be necessary.

(McIntosh adds that sometimes tears freeze, which can make it feel like the eyes are freezing. For more on eye freezing and how it’s treated, check out this article from EyeWorld, published by the American Society of Cataract and Refractive Surgery.)

This NOAA chart is a useful reference for frostbite susceptibility, according to McIntosh, although the temperatures and wind chill numbers are very general and typically refer to tissues most at risk of sustaining frostbite, such as the fingers and nose. “The blood flow to the extremities, and especially the ends of the extremities, is lower than the core (chest, abdomen, pelvis),” writes McIntosh. “When the body gets cold, it shunts blood to the core and away from the extremities in order to sustain life functions. The body would rather lose fingertips than die of a cold heart or brain.”

*The tree Clark’s family picks out is also a blunder. According to this entertaining interview in Rolling Stone with some of the Christmas Vacation cast members, the scene actually took place in Breckenridge, Colorado. I checked in with Ron Cousineau, the Colorado State Forest Service’s district forester for Grandy County, who watched the scene while on the phone with me. He says that the Griswold tree looks like “a perfect Douglas fir.” It has a Douglas fir branching pattern, rather dark needles, and in one shot, the cones look like ones you’d find on a Douglas fir, he says. “[The cones] have this little bracht, kind of like a little tongue hanging out of each scale.”

The thing is, Douglas fir trees aren’t native to Illinois, where the Griswolds supposedly live. Here’s a map of their native range. (We won’t go into the fact that the Griswolds also wouldn’t have been able to dig up a tree that size and strap it onto their car.)

THE SLEDDING SCENE

On one seasonal outing, Clark, his cousin Eddie, and their various offspring take the sleds for a spin. Clark rubs his saucer down with his company’s “non-caloric, silicon-based kitchen lubricant,” which supposedly creates a surface “500 times more slippery than any cooking oil.” Seconds later, he careens down the hill in a fiery blaze, weaving through trees, crossing a busy road, and finally colliding with a gift donation box (or what appears to be) at Walmart.

In the real world, of course, Clark would never go that fast. If there were no friction at all, Clark would be sailing “just normal-fast—no fire,” says former SciFri guest Rhett Allain, author of Geek Physics. (“Clearly they added that for dramatic effect, and I’m okay with that,” he adds.)

But let’s say Clark did go that fast immediately after boarding his sled. He might have celebrated Christmas in the hospital. “There’s two kinds of ways you accelerate—something can push you, or gravity could pull you,” says Allain. In Clark’s case, “there has to be something pushing him to accelerate him to super speeds.” Whether that acceleration came from an unseen rocket or some other hidden propulsion system pushing at Clark’s back, it could have caused his body to compress, potentially leading to internal injury. (Read Allain’s discussion of the physics conundrums facing superheroes here.)

For those more grounded in reality, what’s a reasonable way to improve your own sledding experience?

For one, consider the snow type. “Snow can fall in so many different ways—it can be very wet or very dry,” says Allain. This brief guide to winter sledding from Outside.com recommends packed powder, “which is forgiving but doesn’t act like a sand dune.”

Also, think about your mode of transportation. Clark was onto something with his flying disc.

“I think the best tip for selecting a sled is to get a smooth-bottomed (saucer) sled with the maximum surface area exposed to the snow and to avoid the ones with blades or with narrow runners on the sides unless you are sliding down really icy snow. Otherwise you’ll bury the sled really quickly,” Christopher Stockdale, an associate professor of physics at Marquette University in Wisconsin, writes in an email. “If it is really icy, then you will do slightly better with the sleds with narrow contact edges, but steering will be worse no matter what, as you are likely to have lots of ruts and rough patches.”

He adds, that “adding a teflon coating isn’t going to reduce your friction coefficient much more than what it already is.” (For more of Stockdale’s sledding tips, check out this Chicago Tribune piece.)

THE TREE-LIGHTING SCENE

No Griswold Christmas would be complete without an ostentatious light show. Clark boasts that he’s wrapped his house in 250 strands—consisting of 100 bulbs per strand—of imported Italian twinkle lights. At 25,000, that’s a lot of lights.

Allain investigated this scene for Wired.com. He figured that the lights on Clark’s house are the kind that are big and burn and hot, and estimated their wattage at 6.3 watts per bulb (he based his guess on a Christmas nightlight). Okay, so if Clark has 25,000 lights, each burning at 6.3 watts, the total wattage would be 157,500 watts, or 157.5 kilowatts (kW). That’s a lot of wattage.

Simply put, “powering this from household electricity will [be] challenging,” writes former SciFri guest Eric Wilhelm, founder of Instructables and a mechanical engineer, in an email. Most homes have a 50 to 100 amp main circuit breaker, according to Wilhelm, which corresponds to approximately 6–12 kW of power. Clark’s setup would most definitely trip the breaker, and the little lights would not twinkle. (For more on how circuit breakers work, check out this article from The Family Handyman.)

Could Clark work around the issue? Jamming the circuit breaker closed so that it doesn’t trip, allowing current to run through, would cause the wires to melt or the insulation and surrounding materials to heat up enough to catch on fire instantly, writes Wilhelm. So that’s a bad idea.

He could try powering the lights from a bank of car batteries, Wilhelm suggests. “Car batteries can often do 1,000 cold cranking amps, which means 1,000 amps for 30 seconds at 7.2 volts or more at 32°F,” he writes. “A bank of 22 car batteries could power it, briefly, for 30 seconds. The risk of fire is still there, of course.” [To see where he got this figure, we use the equation P (power) = I (current) x V (voltage). In this case, I = 1,000 amps, P = 157,500 watts, and V = 7.2X volts, where X = the number of car batteries).

Diesel generators might also work. “A 7 kW diesel generator is a manageable size (a small cart), and 22 of them could fit in the front yard. Different from the batteries, they could power the lights in a sustained fashion, but it would be quite noisy.”

In the end, though, the best “no fuss” light show is probably a bonfire, writes Wilhelm. “A good-sized pile of logs easily has the same amount of embodied energy as all those lights running for some reasonable period of time, and the fire department could be encouraged to come before they were really needed.”

*This article was updated on December 24, 2015 to correct a spelling error in the word “Iditarod.” 
*This article was updated on January 13, 2015, to indicate that Eric Wilhelm was interviewed via email.