"Overall gum chewing is more beneficial than it is harmful, " says Dr. Michael Benninger, chairman of the Head and Neck Institute at the Cleveland Clinic in Ohio.

CNN: Chew on this: Gum may be good for body, mind

Before you go getting any bad ideas, know that Benninger and Sobell haven't released the app for public use, and warned both transit systems in late 2011 (though neither region has fixed the exploit, the duo claim).

ENGADGET: Security researchers identify transit system exploit in San Fran and New Jersey, create app to prove it

Creating an Android app named "UltraReset" and using it in tandem with an NFC-enabled Android phone (a Nexus S, in this case), security researchers Corey Benninger and Max Sobell were able to reset and reuse -- free of charge -- transit access cards in both San Francisco's MUNI system and New Jersey's PATH system.

ENGADGET: Security researchers identify transit system exploit in San Fran and New Jersey, create app to prove it