I am with Gorbag; I chew 4-6 pieces of that (used-to-be) nickel bubble gum for a day at a time often, and I dip it in ice-water often to make it very hard to chew. It makes my jaw strong. Jack Demspey advised this and apparently integrated that into his fight training. I also think that it is good cunnilingus workout- my tongue can break boards and shit now from mashing up frozen gum wads.
"Ah, those endless forests, and their horror-haunted gloom! For what eternities have I wandered through them, a timid, hunted creature, starting at the least sound, frightened of my own shadow, keyed-up, ever alert and vigilant, ready on the instant to dash away in mad flight for my life. For I was the prey of all manner of fierce life that dwelt in the forest, and it was in ecstasies of fear that I fled before the hunting monsters."
Jack london, "Before Adam"