I didn’t think anyone would get it. I was completely stumped myself until I got help from my friends. But Neil got it.
In his words, “We have onomatopoeaic words for the sounds made by all of the animals on the right.”
Or, as I prefer to think of it, the animals on the right all have vocabularies (consisting, in most cases, of a single word) while those on the left do not.
A donkey brays, and when it brays it says hee-haw. The donkey makes it to the right of the line not by virtue of braying, but by saying hee-haw. Thus the elephant, which trumpets, but thereby merely makes a noise (as opposed to saying a word) is consigned to the left.
Lions, tigers, and jaguars all roar, but to the best of my recollection from extensive reading (mostly at about age 5), lions and tigers, when roaring, actually say the word “roar”, while a jaguar merely roars incoherently. Chickens say “cheep”. Hens say “buck-buck-buck” (the act of saying this is called “clucking”). Roosters can crow in either of two dialects: Some say “rrr-rr-rrr-rr-rrrrr” while others (who my five-year-old self considered unbecomingly pretentious) say “cock-a-doodle-doo”. Pretentious they may be, but as a scientist, I am here to record the facts, not to judge them.
Regarding some of the side discussions that came up in comments, I have no idea why the count is off at the top of the first column, or whether the jaguar was added at a later time, or if so why.
For the benefit of math_geek, who (in yesterday’s comments) lamented the absence of the okapi, I present another list of about the same vintage as yesterday’s, this time with the columns clearly labeled so that future generations (i.e. us) wouldn’t have to puzzle this one out — and with the okapi well represented:
And finally, I think we should let Andy Kaufman have the last word on this: