Here’s a fact that many people don’t know: octopuses have three hearts—two pump blood to the gills, and the third pumps oxygenated blood to the rest of the body. Also, their blood is blue because it uses copper-based hemocyanin instead of iron-based hemoglobin.
Here’s one little fact that surprises a lot of people:
Your brain can “fill in” missing visual information—so you might not actually see what’s objectively there.
For example, many blind spots in your vision (including the optic disc, where the optic nerve exits your eye) are compensated for by your brain using surrounding context. So even though there’s literally no input from that spot, you typically don’t notice anything missing.
If you want, I can give you a “random” fact in a specific area (space, biology, tech, weird history, etc.).
Here’s a lesser-known fact: Octopuses have three hearts—two that pump blood to the gills and a third that pumps blood to the rest of the body. Also, their blood contains hemocyanin (a copper-based molecule), which is why it’s blue instead of red.