What Was I Thinking?

It was said of me in graduate school that “He’s never happy unless he’s making a list”.

My compulsion to make lists has abated over the years, but it lasted long enough that I still find occasional relics lying around.

Recently I ran across the list reproduced below, dating, apparently from my zoology phase, when I was making lists that classified animals according to various criteria. But I was completely unable to recall what criterion had governed this particular list. What rule places the giraffe on the left and the dog on the right?

I was pretty sure this would remain a mystery forever, but a small consortium of my brilliant friends proved me wrong. None of these friends had known me back in my zoology days, so they had no memories to go on — just the list itself. To my amazement, they reconstructed the pattern. Your challenge is to do the same.

No fair participating if you are part of that consortium that has already solved the problem, though I’m not sure any of those people read this blog anyway.

My memory is a little hazy, but I think the original project might have been extremely important for science.


32 Responses to “What Was I Thinking?”

  1. 1 1 Adam

    The animals on the left are delicious, while the ones on the right are more delicious.

    *tucks in to wolf sandwich*

  2. 2 2 Tom

    Originally I’d thought maybe one side has 39 pairs of chromosomes and the other 30 (can you already tell I’m not a Zoologist?), or that one side was closer to humans in some x than the other side, then wondered if it was weeks for gestation.

    Are the numbers relevant?

  3. 3 3 Harold

    As soon as I saw roadrunner, I thought cartoon characters, but there are plenty of cartoons featuring animals from both sides.

    The numbers almost equal the totals on the list, but there are 40 on the left. Perhaps one was added after the total was put in. That Jaguar looks a bit different.

  4. 4 4 Harold

    The right has “bird” and several individual birds. The left has “eagle”, “pelican” and “penguin”, which are birds, so seem to be on both sides. This would seem to rule out some classification based on the actual properties of the living animals. You also have “chicken” and “hen”, which to me seems a fine distinction.

    Usually, when making a list, one starts with the easy members, and then have to think harder to get the difficult ones. And why did you come back later and add that “jaguar”? It must have struck you after completeing the list that there was another member of the left hand group, and you added it on.

    I was thinking about linguistics – plurals, origin of the words, but I can’t see any pattern there.

  5. 5 5 Mike H

    @Adam :
    The Kangaroo can jump incredible.
    He has to jump, because he’s edible.
    I would not eat a kangaroo,
    but many fine Australians do.
    Those with cookbooks, and with boomerangs,
    enjoy him in tasty kangaroo-meringues.

  6. 6 6 n+2

    I am able to identify many of the animals on the right, but few of those on the left, by the sounds they make.

  7. 7 7 Tom

    Right, so beyond missing the obvious about the numbers…

    The numbers are totals, which means the aim was probably to compare the two sides of the paper, i.e. ‘There are 39(or 40) Xs but only 30 Ys’. Which means that there’s a finite group from which you selected – there are no other animals (which you were aware) which fit on the list as a whole.

    As Harold said, there doesn’t seem to be anything about the actual animals in and of themselves that makes them one or the other.

    Which means we shouldn’t be thinking ‘oh, the left side are nocturnal while the right side are diurnal’, or ‘the left live outside the tropics of cancer and capricorn while the right live between them’. Maybe the key is to find out what unifies all of these animals – or their names, at least.

    Are they all mentioned in the Origin of Species?
    Are the ones on the right all in Aesop’s fables?

    Nope. Still no closer.

  8. 8 8 Harold

    The sounds could be it – or names for the sounds. I could name the sounds most on the right make – not sure about bear. An surely everyone knows that elephants trumpet?

  9. 9 9 math_geek

    Harold, I think that’s a really good guess. Bear’s roar or growl, or so I would guess. I was thrown off by Road Runner, but I must presume that Road Runner is the celebrity road runner, and therefore Meep Meeps. But don’t Jaguars roar? And if roar doesn’t count then what is Lion and Tiger doing on the rightmost list.

  10. 10 10 nobody.really

    Landsburg saw Rex Harrison in the 1967 film Dr. Doolittle, and began pondering which animals he might have a hope of learning to communicate with orally (because he had successfully emulated their sounds), and which he had no hope for.

  11. 11 11 Super-Fly

    I’m thrown off by entries like the non-specific “bird” seeing as how there are numerous other birds on the list.

    Also, how “rooster” and “chicken” are separate entries.

  12. 12 12 maznak

    The list on the right has much higher percentage of domestic or domesticable animals… especially the beginning looks like some of the most obvious domestic or farm animals. But there are too many exceptions for this to be a rule…
    Alternatively, the left list might have been animals Steve has seen on his trip to ZOO, while on the right are animals he did not.

  13. 13 13 Harold

    It was n+2′s guess really.

  14. 14 14 Jeremy N

    I think n+2 is correct; it fits pretty well, but not perfectly. For instance, dolphins and elephants are pretty distinguishable.

    I still question the specificity of some, like chimpanzee or hen vs. chicken vs. rooster. Roosters fits but identifying a hen or chicken?

    I’m not completely satisfied.

  15. 15 15 Tom

    Super-Fly – That’s why it seems like it might have something to do with a book, a TV show or a film. Big bird was a bird, but Fetcher from Chicken Run was a rooster (not a chicken).

    Taking Maznak’s suggestion, it would make sense if the list on the right had a higher percentage of domesticable animals because popular depictions of animals are normally anthropomorphic.

    Are the ones on the right speaking parts in Disney films and the ones on the left non-speaking parts in Disney films? (Films at that point in time…)

  16. 16 16 Harold

    I was thinking films etc., but there have been many made since the list it is difficult to remember what had not been included. The rabbit made me discard this theory, since Bugs is very famous, but of course he is not Disney. And Dumbo, which is Disney, was made a while ago.

    By the way, whats the difference between Bing Crosby and Walt Disney? Bing sings and Walt disney. (Best said in a Scottish accent).

    I keep coming back to that jaguar. If I am right about it being added later, then it must have come to mind to be included. This would suggest a positive list, rather than a negative one (animals which do not…). i still think noises is a good guess, but I can’t see why you would add jaguar on later. After all, even if were not absolutely sure, I would probably guess it sounds a bit like a lion or a tiger, so I wouldn’t go back and add it to a list of animals I do not know the name of their sound.

  17. 17 17 Al V.

    My first thought was that the right was all animals that had appeared in some old book, such as the Bible. But I suspect there are no road runners in the Bible. Second thought was cartoon animals on the right, but rabbit is on the left. In general, the more commonly domesticated animals are on the right, but rabbits (left) are certainly domesticated, while owls (right) are not.

  18. 18 18 Tom

    Harold, you’re absolutely right. Dumbo. And, of course, Thumper now I think of it.

    What I don’t understand is how the total numbers are important, but Jaguar was added later.

    Presumably these lists are intended to be ‘complete’ – that’s why the numbers are important (presumably other animals could be slotted into either side but for one reason or another fail to qualify at all). So all animals that appear must share something in common, be part of a larger group (e.g. all appear in the bible). Then, of that group, the ones on the left are in one sub-group (Old Testament) and the ones on the right in another sub-group (New Testament) (Thanks Al for the idea!). But somehow Jaguar was missed from the group of overall animals.

  19. 19 19 Al V.

    Perhaps a clue – all of the marsupials are on the left: Kangaroo, Possum, Koala. Plus Platypus, which is not a marsupial, but…

  20. 20 20 Neil

    We have onomatopoeaic words for the sounds made by all of the animals on the right.

    I do not know what common feature all of the animals on the left possess (other than we don’t have such words), nor why anyone would keep such a scrap of paper for all these years.

  21. 21 21 Ken B

    @Al V: Ovoviviparian. (Thank you; I pine for the chance to use that word. Like charivari (various spellings exist).)

  22. 22 22 Ken B

    @Neil: If that isn’t the answer it should be! Excellent.

  23. 23 23 Jonathan Campbell

    What sounds does a dove make?

  24. 24 24 Al V.

    Coo. That may be it! For the animals on the left, either we don’t have a word for their vocalization (What sound does an armadillo make?), or the word is not onomatopoeaic, such as trumpet for an elephant’s sound. Dolphins and Guinea Pigs make sounds, but I’ve never heard a name for those sounds.

  25. 25 25 Al V.

    What’s the name for the sounds chimps and road runners make? Do real road runners go “beep beep”?

  26. 26 26 math_geek

    What onomatopoeaic sounds do lions and tigers and bears (oh my) make?

    And why don’t jaguars make them?

  27. 27 27 Neil

    Al V. Chimps grunt. The road runner entry probably reflects Steve’s corny sense of humor. But what about the left side? They are mostly animals with distinguishing physical features (trunks, necks, humps, pouches,stripes, ears, …) but I can’t classify all of them this way.

  28. 28 28 math_geek

    Chimps go Ooo Ooo Ooo I would think, as opposed to an orangotan that goes Ook.

    Neil, I would imagine that an animal is either notable for a physical feature or a sound that it makes, and therefore makes it more known increasing the likelihood that it makes the list.

    on a related note, why an Okapi is not a known animal is not clear to me, because those things are clearly cool.

  29. 29 29 Neil


    You are probably right. If we could discover an animal without a single distinguishing feature, that would be its distinguishing feature.

  30. 30 30 Ken B

    You can make a rule for ANY division of the animals if you try hard.
    If you Godel encode the names of the animals you can construct two polynomials, having those on the left as roots of one and those on the right roots of the other. Godel encode those polynomials and you have two roots of a polynomial Steve was looking at that day.

    Either that or Neil’s answer.

  31. 31 31 Joseph

    I don’t have an answer, but I do have a couple of observations.

    First, I don’t think it is safe to assume “Jaguar” was added after the final count of the left column. Since the line with “Lizard” has the error, this could have been the last item. For some reason it was removed from that side of the list, crossed out, and not counted. It was then added back later.

    Also, since “29″ is crossed out and replaced with “30″ on the right hand side. It seems safe to assume that “owl” was added as an afterthought to this side. (the error next to “Frog” looks like an “F.” If it is not, the same argument as above applies).

    The lists also do not need to be grouped categorically. It could be some sort of logical progression for each list with a random starting point. On the left side, for instance, Giraffe leads to Rhinoceros leads to fish and so one down the list. Whatever the rule, it need not be specific to animals.

  32. 32 32 Harold

    I thought the jaguar looked different – possibly a different pen. I may be wrong, so we cannot be sure that jaguar was the “extra” item.

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