I am preparing an outreach talk about CP violation. I can vaguely remember that there is a (famous?) nature paper about parity violating cows (direction of chewing rotation is not evenly distributed.) I think it could be quite entertaining to use this as a smooth introduction for parity violation (in more serious physics cases) and it would be even nicer, if I could reference this nature paper. Unfortunately, I cannot find it:/ Does anyone know this paper?
I believe the paper you are looking for is the 1927 paper
Movements of the Lower Jaw of Cattle during Mastication. P. Jordan and R. de L. Kronig. Nature 120, 809 (1927),
This is paper also mentioned in the footnote to
The discovery and nondiscovery of parity nonconservation. A. Franklin. Stud. Hist. Philos. Sci. 10, 201 (1979)
(which is how I found it).
Overview of the Paper
Here is a brief overview of the paper (note though that the paper is less then a page long):
- Some things in biology display a definite sense of rotation: e.g. growth of creepers or snail shells. This paper looks at the chewing motion of cows.
- They found in the northern part of Sjaelland, Denmark, 55% of cows chew with a right-circular motion.
So actually there conclusion is that there is no parity violation in cows (since the number of left and right-circular chewers is approximately equal).As correctly pointed out by Emilio in the comments they don't really make any conclusions about the parity conservation due to the size of their data set.
Given that this does not demonstrate parity violation - you could use it as an example of parity conservation and then use the e.g. snail shells as parity violation.