The Mysteries of Animal Movement

David Hu was changing his infant son’s diaper when he got the idea for a study that eventually won him the Ig Nobel prize. No, not the Nobel Prize — the Ig Nobel prize, which bills itself as a reward for “achievements that make people laugh, then think.”

As male infants will do, his son urinated all over the front of Dr. Hu’s shirt, for a full 21 seconds. Yes, he counted off the time, because for him curiosity trumps irritation.

That was a long time for a small baby, he thought. How long did it take an adult to empty his bladder? He timed himself. Twenty-three seconds. “Wow, I thought, my son urinates like a real man already.”

He recounts all of this without a trace of embarrassment, in person and in “How to Walk on Water and Climb up Walls: Animal Movements and the Robotics of the Future,” just published, in which he describes both the silliness and profundity of his brand of research.

No one who knows Dr. Hu, 39, would be surprised by this story. His family, friends, the animals around him — all inspire research questions.

His wife, Jia Fan, is a marketing researcher and senior data scientist at U.P.S. When they met, she had a dog, and he became intrigued by how it shook itself dry. So he set out to understand that process.

Now, he and his son and daughter sometimes bring home some sort of dead animal from a walk or a run. The roadkill goes into the freezer, where he used to keep frozen rats for his several snakes. (The legless lizard ate dog food). “My first reaction is not, oh, it’s gross. It’s ‘Do we have space in our freezer,’” Dr. Fan said.

He also saves earwax and teeth from his children, and lice and lice eggs from the inevitable schoolchild hair infestations. “We have separate vials for lice and lice eggs,” he pointed out.

“I would describe him as an iconoclast,” Dr. Fan said, laughing. “He doesn’t follow the social norms.”

He does, however, follow in the footsteps of his father, a chemist who also loved collecting dead things. Once, on a family camping trip, his father brought home a road-killed deer that he sneaked into the garage under cover of night.

The butchering, a first time event for everyone in the family, he wrote once in a father’s day essay for his dad, “was an intense learning and sensory experience. There were a lot of organs in an animal, I learned.”

His own curiosity has led him to investigations of eyelashes and fire ants, water striders and horse tails, frog tongues and snakes.

Dr. Hu is a mathematician in the Georgia Tech engineering department who studies animals. His seemingly oddball work has drawn both the ire of grandstanding senators and the full-throated support of at least one person in charge of awarding grants from that bastion of frivolity, the United States Army.

Long before his role in the Brett Kavanaugh confirmation hearing, Senator Jeff Flake, Republican of Arizona, put three of Dr. Hu’s research projects on a list of the 20 most wasteful federally funded scientific studies. The television show, “Fox and Friends,” featured Sen. Flake’s critique.

Naturally, Dr. Hu made the attack on his work the basis for a TEDx talk at Emory University, in which he took a bow for being “the country’s most wasteful scientist” and went on to argue that Sen. Flake completely misunderstood the nature of basic science.

Dr. Hu was tickled to think that one scientist could be responsible for such supposed squandering of the public’s money. Neither he nor his supporters were deterred.

Among those supporters is Samuel C. Stanton, a program manager at the Army Research Office in Durham, N.C., which funded Dr. Hu’s research on whether fire ants were a fluid or a solid. (More on that and the urination findings later.)

Dr. Stanton does not share Dr. Hu’s flippant irreverence. He speaks earnestly of the areas of science to which he directs Army money, including “nonequilibrium information physics, embodied learning and control, and nonlinear waves and lattices.”

So he is completely serious when he describes Dr. Hu as a scientist of “profound courage and integrity” who “goes where his curiosity leads him.”

Dr. Hu has “an uncanny ability to identify and follow through on scientific questions that are hidden in plain sight,” Dr. Stanton said.

When it comes to physics, the Army and Dr. Hu have a deep affinity. They both operate at human scale in the world outside the lab, where conditions are often wet, muddy or otherwise difficult.

In understanding how physics operates in such conditions, Dr. Stanton explained, “the vagaries of the real world really come to play in an interesting way.”

Besides, Dr. Stanton said, the Army is not, as some people might imagine, always “looking for a widget or something to go on a tank.” It is interested in fundamental insights and original thinkers. And the strictures of the hunt for grants and tenure in science can sometimes act against creativity.

Sometimes, Dr. Stanton said, part of his job is convincing academic scientists “to lower their inhibitions.”

Needless to say, with Dr. Hu that’s not really been an issue.

An aspiring doctor is led astray

“Applied mathematicians have always been kind of playful,” Dr. Hu said recently while talking about his academic background — although they are perhaps not quite as playful as he can be. A few years ago he did gymnastic flips onto the stage of a Chinese game show that sometimes showcases scientists.

He grew up in Bethesda, Md., and while he was still in high school, he did his first published work on the strength of metals that had been made porous. He was a semifinalist for the Westinghouse Science Prize (the forerunner of the Intel Science Prize) and won several other awards.

That work helped him get into M.I.T., which he entered as a pre-med student planning to get an M.D./Ph.D.

He was soon led astray.

Dr. Hu’s undergraduate adviser at M.I.T. was Lakshminarayanan Mahadevan, a mathematician who works to describe real life processes in rigorous mathematical terms.

Dr. Mahadevan, known to students and colleagues as Maha, investigated wrinkling, for example. Naturally he won an Ig Nobel for that work.

“Maha lit the fire,” Dr. Hu said. Before he encountered his adviser’s research, he said, “It didn’t really make sense that you could make a living just playing with things.”

But he came to see the possibilities.

He stayed at M.I.T. for graduate work, in the lab of his adviser, John Bush, a geophysicist. Dr. Bush remembers him as very enthusiastic.

Asked by email about some of Dr. Hu’s wilder forays into the physics of everyday life, he said, “A sense of playfulness is certainly a good thing in science, especially for reaching a broader audience.” But, he said, “targeting silly problems is not a good strategy, and I know that David has taken considerable flack for it.”

Dr. Hu may be the first third-generation (in terms of scientific pedigree) Ig Nobel winner, because Dr. Mahadevan studied under the late Joseph Keller, a mathematician at Stanford University. Dr. Keller won two Ig Nobels. One was for studying why ponytails swing from side-to-side, rather than up and down, when the ponytail owner is jogging. The other was an examination of why teapots dribble.

After M.I.T., Dr. Hu did research at the Courant Institute at New York University, another hotbed of real-world mathematics. He moved to Georgia Tech, after Jeannette Yen, a biologist there, told the university they ought to take a look at him.

From ants to self-assembling robots

Dr. Hu’s research may seem like pure fun, but much of it is built on the idea that how animals move and function can provide inspiration for engineers designing human-made objects or systems.

The title of Dr. Hu’s book refers to the “robots of the future,” and he emphasizes the way animal motion offers insights that can be applied to engineering — Bio-inspired design.

When Brazil’s Pantanal wetlands flood, for instance, fire ants form rafts so tightly interlaced that water doesn’t penetrate their mass. When he picked up such a mass in the lab, Dr. Hu writes, it felt like a pile of salad greens.

“The raft was springy, and if I squeezed it down to a fraction of its height, it recoiled back to its original shape. If I pulled it apart, it stretched like cheese on a pizza.”

He found out that the ants were constantly moving even though the shape of the mass stayed more or less the same. They were breaking and making connections all the time, and they became, in essence, a “self-healing” material.

The idea is appealing for many engineering applications, including concrete that mends itself and robots that self-assemble into large, complex structures. Depending on the force applied to them, a mass of a hundred thousand ants or so can form a ball or a tower, or flow like a liquid.

He and students in his lab also showed that the reason mosquitoes don’t get bombed out of the air by water droplets in a rainstorm is that they are so light that the air disturbed by a falling drop of water blows the mosquitoes aside. The finding could have applications for tiny drones.

They also showed that the ideal length for a row of mammalian eyelashes is one-third the width of an eyeball. That gives just the right windbreak to keep blowing air from drying out the surface of the eye. Artificial membranes could use some kind of artificial eyelashes.

And what about urination? It didn’t make sense to Dr. Hu that a grown man and an infant would have roughly the same urination time.

After he sent out undergraduates, under the guidance of Patricia Yang, a graduate student, to time urination in all the animals at the Atlanta Zoo, the situation became even more puzzling. Most mammals took between 10 and 30 seconds, with an average of 21 seconds. (Small animals do things differently.)

The key was the urethra, essentially a pipe out of the bladder, that enhanced the effect of gravity. Even a small amount of fluid in a narrow pipe can develop high pressure, with astonishing effects.

Water poured through a narrow pipe into a large wooden barrel can split the barrel. Dr. Hu said the experiment, known as Pascal’s barrel, can be replicated nowadays with Tupperware.

What is interesting about the urethra biologically is that its proportions, length to diameter, stay roughly the same no matter the size of the animal (as long as it weighs more than about six and a half pounds).

The 21-second average urination time must be evolutionarily important. Perhaps any longer would attract predators? But then predators are subject to the same rule. In any case, the principle of how to effectively drain a container of fluid could be useful, Dr. Hu wrote in the original studies, to designers of “water towers, water backpacks and storage containers.”

As usual, in his book Dr. Hu does not neglect the human side of his work, or treat it too seriously. He refers to the urethra as a pee-pee pipe. And he corrects his son when he brags that only he, not his sister, has a pee-pee pipe.

Not so, Dr. Hu insists. The urethra is present in males and females.

Once older, his children may never forgive him for this book. But middle school science teachers and nerds everywhere will thank him.