From "For Home and Country" by Norma Boltin and Angela Herb...
One veteran recalled that army regulations stated "a good set of teeth were necessary for a recruit on account of the necessity of biting the end of the paper cartridge [when loading shot into a rifle], but for this it appeared that only front teeth were required. ... But When ... that wonderful creation... known as the army cracker appeared, this mystery of the requirement of the teeth was fully cleared up. It then appeared that men were selected not for courage or endurance..., but for good grinders." Soldiers had no choice but to survive as best they could on hardtack. Dipping the stale, moldy hard bread in coffee or soup softened it, but also loosened the worms and weevils that typically infested it. So bad was the problem of worm infestation that soldiers came to call teh crackers "worm castles". As one disgruntled man put it, "All the fresh meat we had came in the hard bread."