One of the enduring myths in molecular physics, when talking about chirality as pertains the existence of enantiomers and the differences between them, is that the way cows chew is also chiral, i.e. the up-and-down and the around-in-a-plane movements combine in such a way that you can distinguish a cow chewing from its mirror image. This is mentioned in e.g. Wikipedia, among other resources.

A recent question in the Physics site asked for the source of this factoid, which turns out to be

Movements of the Lower Jaw of Cattle during Mastication. P. Jordan and R. de L. Kronig. Nature 120, 809 (1927),

and this is a rather unsatisfactory source: they report on a survey that finds that 55% of cows chew in a 'right-circular' fashion and 45% chew left-circularly, but they then go on to disavow any statistical significance in the result:

The number of observations was, however, scarcely sufficient to make sure if the deviation [in the ratio of the two kinds] from unity is real.

Given that this isn't a physics question, I thought I'd bounce it over to the mammalian behaviourologists out there: have there been further studies about which way cows chew? I imagine that they're out there, but I wasn't able to find them.

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    $\begingroup$ I'd say as a biologist it's almost as interesting if individual cows indeed chew a constant direction (sort of analogous to 'handedness') versus whether there are population-level biases toward chewing a certain direction. If the former is true, regardless of whether the average cow has a biased direction it makes a reasonable entertaining example. Interestingly, Google Scholar notes just 6 citations of the paper you refer to; all 6 are making the chirality connection, none of them have any association with biology whatsoever. $\endgroup$ – Bryan Krause Jul 12 '18 at 17:45
  • $\begingroup$ @Bryan That's an interesting distinction I hadn't considered. $\endgroup$ – E.P. Jul 12 '18 at 17:55
  • $\begingroup$ It seems there is a commentary on that original article RIEHM, H., & GUGGENHEIM, E. (1928). Movements of the Lower Jaw of Cattle during Mastication. Nature, 121(3045), 357. - they comment that they observe the same direction of chewing in an individual when taking in food and ruminating. They also point out that since the direction of food travel is opposite, the same direction of rotation makes them both left and right handed with respect to food travel. I find that argument a bit silly from a biology perspective but maybe a physicist would appreciate it. :) $\endgroup$ – Bryan Krause Jul 12 '18 at 18:02
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    $\begingroup$ Another related example from biology is hand-clasping: when you interlock your fingers together, which thumb is on top? Individuals have a strong bias. Interestingly, this is independent of left/right handedness, and also independent of arm-crossedness: when you cross arms, which hand goes under and which goes above the upper arm? There is some loose correlation with parents for these traits, but in the overall population they are not particularly biased. $\endgroup$ – Bryan Krause Jul 12 '18 at 18:07

This study deals with the chewing direction of cows. It splits the chewing into three phases, the first jaw movement, the middle ones and the last one. It finds out that the first one is always in the opposite direction of the middle ones, that generally the middle ones are usually in the same direction and that seemimgly cows change chewing direction from one middle jaw movement period to another.

  • $\begingroup$ @BrianKrause here's a partial answer to your comment, even with a small dataset and no statistics attached to it. $\endgroup$ – LinuxBlanket Jul 29 '18 at 6:49

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