When Martin Cohn passed through airport security at Ronald Reagan Airport, he figured that he’d probably get some questions about the 3-D-printed model of a mouse penis in his bag.

The model is 15 centimeters long, made of clear translucent plastic, and indisputably phallic— like the dismembered member of some monstrous, transparent, 11-foot rodent. One of Cohn’s colleagues had already been questioned about it when she carried it on an outward flight from Gainesville to Washington D.C. She put it through the security scanner, and the bag got pulled. A TSA official looked inside, winked at her, and let her go. She was amused but embarrassed, so Cohn offered to take the model home on the return flight.

Once again, the bag was pulled. A TSA officer asked if Cohn had anything sharp or fragile inside. Yes, he said, some 3-D-printed anatomical models. They’re pretty fragile. The officer pulled out two models of mouse embryos, nodded to herself, and moved on. “And then,” Cohn recalls, “she pulled out this mouse penis by its base, like it was Excalibur.”

What is this?

“Do you need to know or do you want to know?” said Cohn.

I’m curious, she replied.

“It’s a 3-D print-out of an adult mouse penis.”

A what?

“A 3-D print-out of an adult mouse penis.”

Oh no it isn’t.

“It is.”

The officer called over three of her colleagues and asked them to guess what it is. No one said anything, so Cohn told them. They fell apart laughing.

Cohn, who’s based at the University of Florida, studies genitals and urinary tracts, and how they develop in embryos. Around 1 in 250 people are born with birth defects affecting these organs, and although such changes are becoming more common, their causes are largely unclear. By studying how genitals normally develop, Cohn’s hoping to understand what happens when they take a different path. And like many scientists, he is working with mice. He recently analysed a mouse’s genitals with a high-resolution medical scanner. To show his colleagues how incredibly detailed the scans can be, he used them to print a scaled-up model, which he took with him to the conference in DC. And because the conference was just a two-day affair, Cohn didn’t bring any checked luggage. Hence: the penis in his carry-on.

Scientists, as it happens, are full of tales like this because as a group, they’re likely to (a) travel frequently, and (b) carry really weird shit in their bags.

In previous years, Cohn has flown with the shin bone of a giant ground sloth and a cooler full of turtle embryos. Just last month, Diane Kelly from the University of Massachusetts, who studies the evolution of animal genitals, was stopped by the TSA because she was carrying what is roughly the opposite of Cohn’s item: a 3-D-printed mold of a dolphin vagina. “Technically it’s not even my dolphin vagina mold,” she says. “I was carrying it for someone.”

Other scientists who responded to a call for stories on Twitter have flown with bottles of monkey pee, chameleon and skate embryos, 5,000 year old human bones, remotely operated vehicles, and, well, a bunch of rocks. (“I’m a geologist. I study rocks.”) Astrophysicist Brian Schmidt was once stopped by airport officials on his way to North Dakota because he was carrying his Nobel Prize—a half-pound gold disk that showed up as completely black on the security scanners. “Uhhhh. Who gave this to you?” they said. “The King of Sweden,” he replied. “Why did he give this to you?,” they probed. “Because I helped discover the expansion rate of the universe was accelerating.”

Anthropologist Donald Johanson has flown with probably the most precious—and the most famous—of these cargos: the bones of the Lucy the Australopithecus, who Johanson himself discovered. In a memoir, he recalls having to show her bones to a customs official in Paris. The man was an anthropology buff, and when Johanson told him that the fossils were from Ethiopia, he said, “You mean Lucy?” “A large crowd gathered and watched as Lucy’s bones were displayed, one by one, on the Customs counter. I got my first inkling of the enormous pull that Lucy would generate from then on, everywhere she went.”

Several people have stories about more animate luggage. Jonathan Klassen from the University of Connecticut studies leafcutter ants, and the permits that allow him to collect wild colonies stipulate that he must hand-carry them onto planes. “Inevitably, some poor security officer gets a duffle bag full of 10,000 ants and gets really confused,” he says. Indeed, many animals have to be hand-carried onto planes because they don’t fare well in the cold of cargo holds, (and often can’t be shipped for similar reasons). That’s certainly the case for the amblypygids—docile relatives of spiders with utterly nightmarish appearances—that Alexander Vaughan once tried to carry onto a domestic flight. “My strategy was to pretend that everything I was doing was perfectly normal,” he tells me.

Others were more upfront about their unorthodox cargo. Ondine Cleaver from UT Southwestern Medical Center once tried carrying tupperware containers full of frogs from New York to Austin. At security, she realized that she couldn’t possibly subject the animals to harmful doses of X-rays, so she explained the contents of her bag to a TSA agent. “She totally freaked out, but had to peek in the container,” says Cleaver. “We opened it just a slit, and there were 12-14 eyes staring at her. She screamed. She did this 3 times. A few other agents came by to see, and none could deal with the container being opened more than a bit. But they had to make sure there was nothing nefarious inside, so we went through cycles of opening the container, screaming, closing it laughing, and again.” They eventually let her through.  

Many scientists have had tougher experiences because their equipment looks suspicious. The bio-logging collars that Luca Borger uses to track cattle in the Alps look a lot like explosive belts. And the Petterson D500x bat detector, which Daniella Rabaiotti uses to record bat calls, is a “big, black box with blinking lights on the front.” She had one in her backpack on a flight going into Houston. “The security people said, ‘Take your laptop out,” and I did that. But they don’t really say, ‘Take your bat detector out,’ and I forgot about it.”

When the scanner went off, she had to explain her research to a suspicious and stand-offish TSA official, who wasn’t clear how anyone could manage to record bat calls, let alone why anyone would want to do that. So Rabaiotti showed him some sonograms, pulled out her laptop, and played him some calls—all while other passengers were going about their more mundane checks. “By the end of it, he said: Oh, I never knew bats were so interesting,” she says.

Many of the stories I heard had similar endings. The TSA once stopped Michael Polito, an Antarctic researcher from Louisiana State University, because his bag contained 50 vials of white powder. When he explained that the powder was freeze-dried Antarctic fur seal milk, he got a mixed reaction. “Some officers just wanted to just wave me on,” he says. “Others wanted me to stay and answer their questions, like: How do you milk a fur seal? I was almost late for my flight.”

Airport security lines, it turns out, are a fantastic venue for scientists to try their hand at outreach. Various scientists are said to have claimed that you don’t really understand something if you can’t explain it to your grandmother, a barmaid, a six-year-old, and other such sexist or ageist variants. But how about this: can you successfully explain it to an TSA official—someone who not only might have no background in science, but also strongly suspects that you might be a national security threat? Can you justify your research in the face of questions like “What are you doing?” or “Why are you doing it?” or “Why are you taking that onto a plane?”

Cohn did pretty well to the four assembled TSA agents who started quizzing him about his mouse penis. They noticed that the translucent object had a white tube inside it, and asked if it was a bone. It was indeed—the baculum. “I explained to them that most other mammals have a bone in the penis and humans have lost them,” says Cohn. “I do outreach at the drop of a hat, and I’m ready to teach a bit of evolution to the TSA if they’re interested. And they were freaking out.”

Eventually, Cohn asked if he was free to go.

You are, said the agent who first looked inside his bag. And then: “I gotta go on break, my mind is blown.”