{"id":3749,"date":"2026-06-20T09:31:00","date_gmt":"2026-06-20T08:31:00","guid":{"rendered":"https:\/\/iop.fnwi.uva.nl\/scm\/?p=3749"},"modified":"2026-09-28T14:26:20","modified_gmt":"2026-09-28T13:26:20","slug":"why-the-poo-emoji-has-its-shape","status":"publish","type":"post","link":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/2026\/06\/20\/why-the-poo-emoji-has-its-shape\/","title":{"rendered":"Why the poo emoji has its shape"},"content":{"rendered":"
\n\"Poo\n<\/picture>
\n The traditional poo emoji (left) only shows one possible shape of faeces. Some worms extrude their excrement upside down, leading to a very different shape (right). As a playful by-product of their work, the authors of the research are planning to design a second poo emoji and officially propose it to the Unicode Consortium. Image: Lukas Kernell, using Nano Banana.
\n<\/figcaption><\/figure>\n

Already in 1881, Charles Darwin marveled at the neat spiral-shaped faecal castings of earthworms. However, he never understood why these faeces take their fascinating, tower-like shapes. Now, physics has provided the answer\u2014and it explains both Darwin\u2019s original observations and the shape of the modern poo emoji.<\/p>\n

\n\"Darwin\"\n<\/picture>
\n Drawings of earthworm poo from Darwin\u2019s 1881 publication \u201cThe formation of vegetable mould through the action of worms, with observations on their habits.\u201d
\n<\/figcaption><\/figure>\n

Most animals defecate downward. As their faeces coil, the pile grows higher and the fall height decreases, making each successive coil smaller. This creates the characteristic pointy mound\u2014precisely the shape of the poo emoji. Lugworms, however, defy gravity by extruding their faeces upward. A new study by physicists Mehdi Habibi (Wageningen University and Research), Neil M. Ribe (CNRS\/Universit\u00e9 Paris-Saclay) and Daniel Bonn (University of Amsterdam), published in Nature Communications this week, reveals something remarkable: the lugworms operate in a previously unknown physics regime where coil size is independent of height \u2013 exactly as Darwin observed. The coil radius stays constant, creating uniform spirals rather than tapered mounds.<\/p>\n

\n\"Poo\"\n<\/picture>
\n The excrement of a lug worm takes a shape that can be explained by the physics and mathematics of coiling ropes. Image from the publication.
\n<\/figcaption><\/figure>\n

The researchers found that both types of faeces obey the laws of elastic rope-coiling theory<\/em> \u2013 as the name suggests, a mathematical description of how ropes and other materials coil. It turns out that the only differences that cause the two types of shapes are the stiffness of the material and, most importantly, the direction of gravity compared to the direction of extrusion. The observations \u2013 and their mathematical underpinnings \u2013 do not just hold for faeces: the researchers tested their ideas on lugworms, on extruded pea dough \u2013 a mix of chickpea flour and water similar to the wet sand of the worm poo \u2013 and even on pasta, and confirmed that different directions consistently lead to the characteristic different shapes. Darwin may have been sad to learn this: evolution, it turns out, doesn\u2019t design waste disposal. Physics does.<\/p>\n

Publication<\/h2>\n

Coiling of lugworm feces reveals universal mechanics for the shape of poo<\/em><\/a>, Mehdi Habibi, Neil M. Ribe, and Daniel Bonn. Nature Communications 17<\/strong>, 5449 (2026).<\/p>\n

Source: IoP news, University of Amsterdam<\/a><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

Ask a child to draw some poo, and the shape will invariably be the same: a coil, broad at the base and pointy at the top, similar to a spiral swirl of soft-serve ice cream. In fact, the often-used poo emoji has this exact shape, as do most actual mounds of faeces found in nature. Exceptions occur, though: in particular, in the faeces of some worms, that extrude their excrement \u2018upside down\u2019 from the ground. As it turns out, there is remarkable physics behind these differences in poo shapes.<\/p>\n","protected":false},"author":1,"featured_media":3748,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[10,20],"tags":[],"_links":{"self":[{"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/posts\/3749"}],"collection":[{"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/comments?post=3749"}],"version-history":[{"count":1,"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/posts\/3749\/revisions"}],"predecessor-version":[{"id":3785,"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/posts\/3749\/revisions\/3785"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/media\/3748"}],"wp:attachment":[{"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/media?parent=3749"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/categories?post=3749"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/iop.fnwi.uva.nl\/scm\/index.php\/wp-json\/wp\/v2\/tags?post=3749"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}