(Photo via War Eagle Reader)
The rabbits in the novel Watership Down can count up to four. Any number higher than that is "hrair", which means "more than four" but is often translated as "a thousand."
This is not dissimilar to the way in which many technologically primitive human societies count. Michael Erard writes in the magazine Science:
For some cultures, big numbers just don’t make sense. Take the shepherd who knows that he has the right number of sheep not by counting them one by one but by grasping the gestalt of his flock. That may sound strange to people from other cultures, says Patience Epps, a linguist at the University of Texas, Austin. Indeed, she says she’s often asked by incredulous Americans how people with few numerals know, for instance, how many children they have. When she asks this of the Amazonian tribe she works with, “they look at me like it’s a weird question. They list the names, they count on their fingers, but they don’t go around with a quantity in their heads,” she says.
From her research the Amazon, Epps found that once tribes began regularly trading with each other, higher numbers became a necessity. The tipping point in number formation, linguist Claire Bowern found in her study of a group of Australian languages, is the number five:
Surprisingly, they tended to acquire numerals in bunches, leaping from five numerals to 10 or 20, for example. The numeral five was often the tipping point—once a system reached five, it was likely to add more numerals, up to 20. As a result, numeral systems with five as an upper limit are rare in Pama-Nyungan languages.
“This is surprising, given the predominance of fingers and toes as things to count,” Bowern notes. Adding or losing the numeral four was the most frequent change. (The words for “four” were most often composed out of words for “two,” not by creating or borrowing a new word that means “four,” showing how the numeral systems evolved.)
Bowern thinks that numerals were added in clusters for practical reasons: If you need to count above five, you probably need to go higher than seven or eight as well. And she speculates that perhaps a cognitive shift occurs at about five. “Once you generalize beyond five or so, it becomes easier to generalize to an infinite system.”
-via Ace of Spades HQ