In 1921 Charles Purdy worried that modern foods require too little chewing, resulting in “decayed teeth, undeveloped jaws, and various other complications due solely to the lack of exercise attendant on proper mastication.”

The answer, he decided, was a bite plate that can be attached to the wall by a spring. “By movements of the head, the device will receive a series of short jerks or impulses which will be transmitted to the teeth in order to produce a strain thereon, which strain serves to give the several organs of the mouth and head a proper exercise to maintain the necessary circulation therein.”

When used in tandem, as shown, this has all the makings of a romantic candlelight interlude as the exercisers “pull in opposite directions similar to the so-called ‘tug-of-war.'” What did this sound like?