Here’s a surprising one:
Octopuses have three hearts. Two pump blood through the gills, and the third pumps it through the rest of the body. When an octopus swims, the main heart actually stops beating, which is one reason they often prefer crawling—it’s less exhausting.
A “jiffy” is an actual unit of time in some scientific contexts: it can mean one-hundredth of a second.
In physics and computing, though, “jiffy” has had different definitions depending on the field—so it’s both a real unit and a delightfully imprecise-sounding one.
Here’s a niche one: octopuses have three hearts.
Two pump blood through the gills, and the third pumps it to the rest of the body. When an octopus swims, the main heart temporarily stops beating, which is one reason they often prefer crawling—it’s less exhausting.