Comment on ''Dogs are sensitive to small variations of the Earth's magnetic field'' Ludek Pekarek, National Institute of Public Health 17 March 2014 In the commented paper , Hart et al. claims to provide proof (based on a statistical evaluation of more than 7000 observations of dogs) of: axis alignment of a dog's body with geomagnetic field lines during defecation or urination, loss of this ability if the fluctuations of the Earth's magnetic field declination exceed a rate of 0.02 arc minutes per minute of time (in  written in percentage terms as 2 %, without repeating the dimension). In this comment we show that neither the north-south alignment of the dogs nor the disturbance of their anticipated magnetic sensing has been proved in . The major argument leading to this conclusion lies in the miniscule value of the declination change rate that was in  considered sufficient for disrupting the assumed magnetic sense. It should be pointed out here that any movement of the dog that has a rotation component relative to ground will change the angle between its body axis and the position of magnetic north. In the reference frame rotating with the dog, this would necessarily be perceived as changing the angle of magnetic declination. Even the rotation by just one arc degree per second (one revolution per 6 minutes, i.e. much less than a dog routinely performs) will by orders of magnitude exceed the rate of change at the largest ever encountered fluctuation of magnetic declination. Furthermore, even if the dog were to stay motionless, imperceptible but unavoidable movements of its body still would create fluctuations of the angle between its body axis and the north-south direction at a rate larger than a geomagnetic storm. To give a particular example, if the backside of the dog would not move, while its nape (say, 0.5 m apart) was moving in the horizontal plane with velocity as small as 1 millimeter per a second of time, the rate of change of the angle of declination observed from the dog’s reference frame would approximately be equal to 40000 % in the units used in  (compare to 2 % claimed in  as disrupting).Apart from the fundamental overlook mentioned above, no details are given in  about the procedure for assigning the quiet regions of declination to the observed cases of north-south orientation (about 20 % of the observations). In addition, it was scarcely possible to keep the double blind method during this crucial step of evaluation, and strong bias could not be avoided. The uncertainty concerning the appropriateness of the categorization is therefore high. The double blind procedure also could not have been applied during the primary observation, as the dog observers knew what outcome was expected from the whole experiment. In brief, the double blind method was not fulfilled at several steps in the experiment and its evaluation.In conclusion, the idea of the assumed magnetic sense of dogs being disturbed by fluctuations of magnetic declination, quoted as the main discovery achieved in , must be rejected. In particular, the suggested far-reaching consequences challenging biologists and physicians “to seriously reconsider effects magnetic storms might pose on an organism” or “When extrapolated upon other animals and other experiments and observations on animal magnetoreception, this (i. e. the claimed disturbing effect of fluctuations of Earth's magnetic field) might explain the non-replicabilty of many findings and high scatter in others”, must be regarded as unsubstantiated. Hart et al.: Dogs are sensitive to small variations of the earth’s magnetic field. Frontiers in Zoology 10, 80 (2013)AuthorsLukas Jelinek (CTU FEE Prague), Ludek Pekarek (SZU Prague) Competing interests Authors of this comment are not aware of any competing interests with respect to the authors of the commented paper.