Check this:
In their write-up of the experiment, Houpt and Smith noted something peculiar. When the rats that got the real magnetic bath were returned to their cages, they immediately began a rapid, nose-to-tail circling—and all in a counterclockwise direction. Some of the animals rotated 30 or more times before settling down. None of their control counterparts exhibited anything like that.
The gene expression analysis had clearly suggested that the inner ears of the exposed rats were being affected by the magnetic field. Perhaps this explained the curious circling behavior—like kids wobbling off a merry-go-round, the rodents were just plain dizzy. This squared, too, with anecdotal reports of nausea and vertigo from MRI technicians and others having to work near big magnets.
The circling itself was interesting, but why the consistent direction? Why did all the dizzy rats rotate counterclockwise?
For answers, Houpt and Smith studied the design of their experiment. To keep a lid on the variables, they had made sure all the rats were inserted into the magnets precisely the same way—with their heads pointed toward the ceiling. This meant the animals' heads were consistently aligned with the magnet's internal southern pole.
On a whim, the researchers decided to try the experiment again, but this time with the rats turned upside down. Magnet-wise, this time all animals were facing north. When the animals were returned to their cages, every one of them began turning.
Clockwise.
http://www.research.fsu.edu/researchr/issue2001/mice.html