Looks like they are testing the effects of certain drugs on the jaw movements of rats. That would require more in depth reading than I'd care to do right now. Why don't you read the article or Google for more:

Originally Posted by http://www.ncbi.nlm.nih.gov/pubmed/14571282

This study tested a system for monitoring jaw movements in freely moving rats. A Hall-effect transducer was fixed to the skull in order to sense voltage changes induced by variations in the position of a magnet fixed to the mandible. By measuring dopamine receptor-mediated jaw movements, this system produces data comparable to that obtained using a light-sensitive transducer system in anesthetized rats, while also measuring the vertical component of jaw movements in freely moving rats. In combination with conventional visual observation, this system may provide a useful tool for assessing movements of the orofacial region during spontaneous and drug-evoked behavior.

Ideas about what? Rats have been used for worse than this for a long time.