Sunday, December 2, 2012

The 250 lb. Hamburger

“…so when a snake eats its prey, it’s like if you were to eat a 250 lb. hamburger, all in one bite, without using your arms!”

It’s 1997, I’m an English major at UC Berkeley, and I’m sitting in a classroom in the palatial Valley Life Sciences Building. This is a building that English majors do not frequent. The shiny white pillars hurt our bookish eyes. Yet I keep coming back, week after week, to a classroom filled with big cat skulls, stuffed egrets, and pickled frogs. By some fluke I have enrolled in a class called Natural History of the Vertebrates, which has nothing to do with my major. It is here that I first witness the hamburger magic trick.

Fifteen years later, the magic trick is still fresh in my mind. And magic it is. Not the rabbit-in-the-top-hat, saw-your-assistant-in-half kind of magic, but real-life magic. Teaching magic.

Making an analogy that allows students to see something from their point of view.
Magic, like most things in life, works best when greasy food is involved.

In that classroom at UC Berkeley, and in countless classrooms before and since, Dr. Harry Greene used the hamburger trick to help students understand one of the most mind-boggling processes in nature: how a snake with a mouth the diameter of a walnut can ingest a rabbit the size of a football… all with no hands.

A Western Diamond-backed Rattlesnake eats a large rabbit. 
J. Schofer

The hamburger trick, friends, is the subject of this post.

So how in the heck does a snake pull off this feat? Let’s start with the meat of it all—or rather, the bones and ligaments.

First things first: it is important to come to terms with the fact that our human skulls are boring.

In contrast, a snake’s skull is a thing of beauty and complexity—by all accounts, an exemplary marriage of structure and function, a marvel of evolution.
The skull of a Gaboon viper boasts impressive two inch-long fangs.

This post is an appetizer version of how-the-snake-skull-works. Keep in mind that I am greatly simplifying the following descriptions—another magicky thing us teachers try to do.

Here's how it works. Your jawbone (or mandible) is functionally a single bone. It articulates with your cranium in joints on either side, in front of your ears, that allow limited rotational movement of the jaw, allowing you to bite, chew, talk, etc.
"The last thing I remember, I was looking at a human skull in anatomy class. I must have died of boredom."

The setup is far more interesting in snakes. The jaw does not attach directly to the rest of the skull, but rather suspends from the skull via the quadrate bone. (You kinda have a quadrate bone, too, but it has migrated, over millions of generations, into your ear—a "hear bone.") 
The large quadrate bone in a reptile skull is shown at left. 

So, think of it as snakes having their jaws suspended from the rest of the skull via a mobile quadrate bone. The snake's quadrate bones can basically whirl around on each side. This funky attachment makes the snake’s mouth far more flexible than yours, and also makes the opening larger.

An egg-eating snake routinely eats eggs several time the diameter of its own head. Notice how the skin stretches between the scale rows. Read this blog for more on egg-eating snakes.
B. Bouton

Still not a big enough hole for Peter Rabbit, though. The trick is in the joint at the front of the jaw bone. Your jaw actually consists of two bones (dentary bones) that fuse together at this joint when you’re a fetus. In a snake chin, the dentary bones are connected with a stretchy ligament that allows the two sides of the jaw to stretch away from each other, allowing the mouth to open even larger.

This image from Digimorph shows nicely how the two dentary bones of the lower jaw are not connected with bone.
You can see the two sides of the jaw stretched far apart in this image of a python gorging on a sheep.

The articulation of the quadrate bone plus the elastic ligament at the chin allow the python's mouth to open large enough to eat huge prey— like deer, crocs... even humans

There’s much more to it than that—other moveable skull bones, super-stretchy skin, even a snorkel to help breathe while the maw is stuffed (yes, really!)—but I am hungry for a hamburger. 

(Note that snakes' jaws do not "unhinge" or "dislocate." Those are entrenched myths that arose from people trying to compare their jaws with our jaws. Let's keep it real, people.)
The upshot of the structural adaptations I have described above is that snakes can stretch open their mouths really wide—wide enough to ingest prey many times the diameter of their own head. Now we are ready for the main course:

“…so when a snake eats its prey, it’s like if you were to eat a 250 lb. hamburger, all in one bite, without using your arms!”

Sadie helps show us what a Macrostomatan Harry would look like sucking down a beast-sized burger. 
J. Furman

That’s a big burger. (A mere fraction of the world record burger, weighing in at a ton, but a big burger nonetheless.)

The record largest burger was made at a Minnesota casino in 2012. It had to be flipped with a crane. But I digress...

Now you can put it all together and watch Harry doing his magic here:

Abracadabra! That is how the magic is done.

Getting hungry? Eat like a snake.

Note: Harry Greene's book Tracks and Shadows: Natural History as Art came out in 2013. If you're still hungry, pick up this book (or his 1997 classic Snakes: The Evolution of Mystery in Nature) to read about some more amazing things snakes do!


Katie Kleber said...

AWESOME! i think i need to add this to my class tomorrow (and i used it in an interview today!)...thank you!

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CloudyHue said...

You'll probably never end up seeing this, but I found it interesting that someone used the video I was in in 5th grade in their blog post. Yep, I'm the little girl there. I found this after looking up my name on a whim.

harada57 said...
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