Give me a list of 20 exciting but very esoteric and widely unknown facts.

Here are 20 lesser-known facts from the stranger corners of biology, mathematics, physics, and history:

1. One deep-sea snail makes armor out of iron minerals. The scaly-foot gastropod, Chrysomallon squamiferum, lives around Indian Ocean hydrothermal vents. In some populations, iron sulfides reinforce both its shell and the protective scales covering its foot.

2. Some bacteria function as living electrical cables. “Cable bacteria” form multicellular filaments that conduct electrons over centimeter-scale distances. This lets them link sulfide-rich sediment to oxygen near the surface—connecting chemical reactions occurring thousands of cell-lengths apart.

3. A complex cell can survive without any mitochondrial organelle. The single-celled organism Monocercomonoides exilis has neither mitochondria nor their reduced remnants. It gets by partly because a system acquired from bacteria performs an essential cellular task normally associated with mitochondria.

4. Some animals manufacture cellulose. Tunicates—marine animals more closely related to vertebrates than to jellyfish—produce cellulose for their outer covering. Their cellulose-making machinery appears to trace back to an ancient transfer of genetic material from bacteria.

5. A squid empties most of its bacterial flashlight every morning. The Hawaiian bobtail squid houses luminous bacteria that help camouflage its silhouette at night. Around dawn, it expels most of them; the remaining population multiplies to replenish the light organ.

6. Some viruses exploit other viruses’ factories. The Sputnik virophage reproduces inside the cellular factories built by certain giant viruses infecting amoebae. Its presence can interfere with the giant virus’s reproduction.

7. Some worms deliberately delete parts of their genomes while developing. In Ascaris roundworms, cells destined to form the body discard specific DNA sequences, while the reproductive lineage retains them. Different cells in the same animal therefore inherit different genomic contents.

8. A seaweed that looks like a miniature plant can be one enormous cell. Caulerpa has structures resembling leaves, stems, and roots, yet its body is largely a single continuous cell containing many nuclei—not a collection of ordinary plant cells.

9. A mathematical function can hit every real number inside every tiny interval. Conway’s base-13 function has this property: however narrowly you restrict its input to an interval of positive length, its outputs still include every real number. It is far stranger than merely being discontinuous.

10. A sphere can be turned inside out without tearing or creasing it. In mathematics, a sphere eversion does exactly this. The crucial permission is that the idealized surface may pass through itself—something a physical rubber ball cannot do.

11. A disk around two stars can orbit almost perpendicular to their orbit. In the quadruple-star system HD 98800, astronomers have observed a gas-and-dust disk in a nearly polar configuration around one stellar pair. It circles roughly over their orbital poles rather than lying in their orbital plane.

12. Two moons of Saturn repeatedly exchange inner and outer orbital positions. Janus and Epimetheus follow almost the same orbit. About every four years, their gravitational interaction causes the inner moon to move outward and the outer moon inward, keeping them from colliding.

13. The first atomic-bomb test accidentally manufactured a quasicrystal. Researchers discovered one in red trinitite, material formed during the 1945 Trinity explosion. Its atoms exhibit an ordered arrangement that does not repeat periodically like an ordinary crystal.

14. Helium refuses to freeze merely because you make it colder. At ordinary pressure, helium remains liquid as its temperature approaches absolute zero. Quantum motion prevents solidification; substantial pressure is needed to make it solid.

15. Water can become a solid framework with mobile hydrogen ions inside. Under extreme pressure and temperature, superionic ice has oxygen atoms arranged in a solid lattice while hydrogen ions move through it. Experiments have produced this unusual, electrically conducting state.

16. Earth once operated natural nuclear reactors—and some apparently pulsed. Around two billion years ago, uranium deposits at Oklo, in present-day Gabon, sustained nuclear fission. Isotopic evidence suggests that some operated in cycles of roughly 30 minutes of activity followed by about 2½ hours off, regulated by groundwater.

17. Ancient Mesopotamians put clay documents inside clay envelopes. Some contracts and administrative tablets were enclosed in an outer clay casing, often bearing seals or repeated text. Opening the casing could reveal the protected original and leave evidence that it had been accessed.

18. Revolutionary France briefly made decimal time official. The day was divided into 10 hours, each containing 100 minutes of 100 seconds. Introduced in 1793, the system prompted the manufacture of special clocks, but its compulsory use was suspended in 1795.

19. The ancestor of the fax machine predates the telephone. Alexander Bain patented an early electrical image-transmission system in 1843—33 years before Alexander Graham Bell’s famous telephone patent. Practical commercial fax services were operating in the 1860s.

20. Economists once modeled national economies using flowing water. The MONIAC, developed by Bill Phillips in 1949, was an analog computer whose tanks, pipes, and valves represented economic quantities and flows. It could demonstrate how changes in taxation, spending, and saving affected the model economy.