The same underlying mechanism was initially considered to be responsible for the influence of the local geomagnetic field (LGF) in the in vitro chick-brain experiments of Blackman et al and the in vivo rat behavioral experiments of Thomas et al. However, subsequent work with the chick brain model showed that the effective LGF vector was effective only when there was a component orthogonal to the alternating field, while recently published results with an in vivo diatom model showed that a parallel orientation was required. A review of the exposure conditions in the rat behavioral experiments provides evidence that supports both the orthogonal and the parallel field components as potential bases for the phenomenon. Investigators who attempt to replicate the rat behavioral experiments must be aware of the conflicting exposure conditions that can be assumed to be operative, and design their experiments accordingly. Further testing is necessary to resolve the issue.