Scientists have explained why the poo emoji looks the way it does

It turns out this isn’t just a designer’s fantasy, nor is it a secret conspiracy by soft-serve ice-cream manufacturers. There is physics behind this familiar shape: when a soft material is dispensed and falls under the influence of gravity, it can naturally twist into a spiral. This is exactly what happens with the faeces of many animals, dough, pasta and even experimental mixtures in the laboratory.

The study has been published in *Nature Communications*.

The authors were not studying the emoji itself, but the actual mechanics: why a soft ‘strand’ of substance, when squeezed out, does not just fall haphazardly but forms neat coils. However, the poo emoji turned out to be an almost perfect illustration of this science.

Details

If you ask a child to draw a poo, they will almost certainly depict a mound: a wide base, coils, and a pointed top. The classic emoji looks much the same.

Physicists explain this quite simply. In most animals, excrement is expelled downwards. At first, the material falls from a greater height and forms a wide lower coil. Then the pile grows, the distance to the top becomes shorter, and the subsequent coils become narrower. This is how the familiar shape emerges: a large base, then getting smaller and smaller, until only the ‘final touch’ remains at the top.

But there are worms that do the exact opposite. Arenicolid marine worms extrude their excrement upwards out of their burrows. In this case, gravity acts differently in relation to the direction in which the material is expelled, and the resulting shape is not a classic tower but a more uniform spiral.

What’s Darwin got to do with it?

Back in the 19th century, Charles Darwin drew attention to the neat spiral mounds left by earthworms. He studied earthworms and was struck by how organised their tracks looked on the surface of the earth.

But at the time, they couldn’t explain why these mounds turned out exactly like that. Now physicists have effectively provided the answer: it’s not that earthworms are secret sculptors, but rather down to how soft material behaves when it’s squeezed out.

To put it simply: the worm does its job, and physics takes care of the result.

Why this works with more than just poo

The funniest thing about this story is that it’s not just about excrement. Scientists tested the idea on various materials: the faeces of marine worms, a mixture of chickpea flour and water—similar in properties to damp sand mixed with worm faeces—and pasta. The result turned out to be similar: if a soft thread emerges under certain conditions, it twists according to the general rules.

This is known as the mechanics of elastic filament twisting. Imagine a soft string being squeezed out of a tube. It doesn’t always lie in a straight line. Sometimes it starts to form loops because the material still retains its shape but is already too soft to lie flat.

That is precisely why worms, pasta, Darwin and emojis all coexisted quite happily in one scientific story.

Why shapes vary

The main factors are how soft or stiff the material is, the speed at which it emerges, and the direction of gravity.

If the material emerges downwards, as with most animals, the result is the familiar ‘pyramid’ shape with coils. If the material is squeezed upwards, as with some worms emerging from their burrows, the coils may be more uniform in size. That’s why the authors even joke that the classic emoji shows only one variation, whilst the world might need a second one — an ‘upside-down’ version of the worm-like one. Researchers from the University of Amsterdam write that the authors plan to propose such a second poo emoji to the Unicode Consortium.

In other words, the poo emoji may be scientifically incomplete. It now has a rival from below. Or, to be more precise, from underground.

Why this matters

At first glance, this is the perfect example of ‘scientists with too much time on their hands’. But in reality, the work relates to the physics of soft materials.

Such processes are important not only for biology, but also for understanding how pastes, gels, dough, mud, biomaterials and any substances that appear to flow whilst still partially retaining their shape behave. *Nature Communications* describes the work as an investigation into the mechanics of faecal shape and the different bending regimes that occur when soft biological material is extruded.

In other words, yes: the scientists studied the shape of a poo. But behind this lies fundamental physics that can be applied to a much wider range of materials.

Background

Arenicolid marine worms live in burrows and extrude processed sand and organic material onto the surface. These spiral mounds are clearly visible on shorelines and have long attracted the attention of naturalists.

The authors of the new study have shown that such shapes can be described by a general mechanical model. It is not the animal’s ‘intentions’ that matter, but the properties of the material and the conditions under which it is expelled.

Source

Study: Mehdi Habibi, Neil M. Ribe, Daniel Bonn — “Coiling of lugworm faeces reveals universal mechanics for the shape of poo”, Nature Communications, 2026.