Have you ever heard of a "pee-pee boy"?
No, I'm not kidding—that's what they're called, and they do exactly that. When I first stumbled across a scientific paper about these little ceramic figures, I couldn't believe someone had actually done serious mathematical work at the intersection of thermodynamics and tea culture. I mean, "pee-pee boy" and "thermodynamics" in the same sentence? That's not something you see every day.
I've actually seen these before, years ago when I was living in China. Back then, I never bothered to be curious about how they peed—I just thought they were funny little decorations. I even have an elephant tea pet sitting on my shelf right now (not a pee-pee boy, just a regular elephant that I pour leftover tea on when it's lost its taste). But reading this research made me realize there's so much more going on here than I ever imagined.
Before we dive into the peeing physics, let me explain what tea pets actually are. Tea pets (茶宠, cha chong) are small unglazed clay companions that live on Chinese tea tables. They're traditionally made from Yixing purple clay—that special reddish-purple ceramic from Yixing county that contains about 9% iron oxide.
The practice of "raising" these pets is called yanghu (养壶), which means nourishing or raising the pot. You repeatedly pour tea over them, and over time, the tea tannins soak into the porous clay, creating a beautiful shiny patina. Some people believe that through this repeated feeding, tea pets gain a "soul"—transitioning from inanimate objects to spiritual companions on your tea journey.
For me, honestly, I'd rather drink the tea unless it's lost its taste. Then my elephant gets it.
Okay, so here's where it gets interesting. I'm going to spare you some of the technical details because I honestly don't intuitively understand all of it myself, but this small figurine is actually hollow. There's a space in it filled with air, and when someone pours hot water over its head, the magic—or rather, the science—happens.
Here's the basic idea:
1. The pee-pee boy has an air pocket in his head
2. Hot water heats the ceramic, which heats the air inside
3. Hot air expands (basic physics: things get bigger when heated)
4. The expanding air pushes down on water in the body
5. Water shoots out the... anatomically correct exit point
And here's the kicker: by measuring the distance of the pee, you can determine whether your water is hot enough for the type of tea you're drinking. The hotter the water, the farther the stream goes. MIT engineers found it's accurate to about 3.7cm per degree Celsius—precise enough to distinguish between water that's perfect for green tea (80°C) versus too cool (60°C).
This is my favorite part of the whole research. These MIT engineers actually figured out the ideal design features to make the pee go far:
- Big head, thin skin: More air to expand, faster heat transfer
- Optimal hole size: About 0.5-1mm (too small and it won't work, too big and no pressure builds up)
- 45-degree angle: Basic projectile physics for maximum distance
- Light for his size: Low "body mass index" (yes, they actually calculated the BMI of ceramic boys)
The traditional Yixing pottery technique of beating clay until it's leather-hard and only 2-3mm thick? Turns out that's exactly what you need for optimal performance. Whoever came up with the idea of making a pee-pee boy had great humor, but it's amazing that they almost seemed to understand the science behind it.
## A Quick History Correction
Now, the original scientific paper suggests these might be the world's first thermometers, predating Galileo's 1592 invention. They mention a Tang Dynasty frog whistle as evidence. But here's the thing: that Tang frog was glazed pottery, not an unglazed tea pet. True tea pets emerged during the Yuan Dynasty (1206-1368), centuries after the Tang period. So while the physics principle might be ancient, tea pets as we know them aren't that old.
Look, I know it's easy to giggle at ceramic boys peeing. But here's what struck me: Chinese tea culture valued temperature precision so much that artisans developed this ingenious—if cheeky—way to measure it. Different teas need different temperatures:
- Green tea: 75-80°C
- Oolong: 85-90°C
- Black tea: 90-95°C
- Pu-erh: 95-100°C
Having a playful, functional tool that could distinguish these temperatures shows how sophisticated tea preparation was, even centuries ago. It's engineering disguised as humor, functionality wrapped in whimsy.
Recently, I've been seeing objects that are seemingly tea pets but with more untraditional—even creative—shapes. I've spotted Marvel characters, anime figures, and all sorts of modern designs sitting on tea tables. And maybe this is me being orthodox, but it made me wonder: should we consider these tea pets as well?
The definition we've been using—small unglazed clay companions made from Yixing purple clay—doesn't actually specify what forms or shapes they should take. But in Chinese tea culture, traditional designs carry specific meanings. The elephant on my shelf symbolizes good fortune. Dragons represent power. Toads attract wealth. Even our cheeky pee-pee boy serves a practical purpose alongside his humor.
So when I see an Iron Man figurine made from purple clay, getting his patina from repeated tea pours, is that still a tea pet? Or is it something else—a hybrid of traditional practice and modern pop culture? I honestly don't have the answer. Maybe the soul a tea pet gains through yanghu doesn't care if it's shaped like a traditional toad or like Spider-Man. Or maybe something essential is lost when we replace symbols with thousands of years of meaning with characters from last decade's blockbusters.
What I do know is that contemporary Yixing artists are still making traditional forms—including our water-spraying friends like frogs, dragons, and tortoises that work on the same thermodynamic principle as the pee-pee boy. These remain legitimate and celebrated parts of Chinese tea culture, their cheekiness notwithstanding.
Let's appreciate one more thing about tea culture that you probably take for granted or at least remains unnoticed because you're probably laughing at the humor. These aren't just novelty items—they're a perfect example of how our ancestors embedded sophisticated understanding into everyday objects. They made the practical playful and the playful practical.
Honestly, how nerdy those MIT engineers were about something I perceived as a simple object both surprises and inspires me. As someone currently learning mathematics with the tentative dream of writing about "The Hidden Geometry of Yixing Teapots," seeing how they mathematically analyzed and applied their knowledge to tea culture shows me what's possible when you look at traditional objects through a scientific lens.
Sometimes the most profound innovations come packaged in the most unexpected forms. In this case, that form happens to be a small ceramic boy doing what small boys do.
Who knew that the intersection of thermodynamics and toilet humor could teach us so much about innovation, culture, and the playful ingenuity of our ancestors?
---
P.S. - If you have a pee-pee boy at home, try this: Pour water of different temperatures on his head and measure the distance. You've got yourself a legitimate thermometer. Just maybe don't mention to your guests that you're using 13th-century toilet humor to check if the water's ready for your tea.
---
Lee, V., & Attinger, D. (2016). Thermodynamics and historical relevance of a jetting thermometer made of Chinese zisha ceramic. *Scientific Reports*, 6, Article 28609. https://doi.org/10.1038/srep28609