"The Diadem sat on the ears and whispered to the brain to drive the wearer mad, probably to the conclusion of suicide. The snake was simply a thoughtless mistake, using a living host. But Tom was desperate by that point and barely clinging to life, not sure if his other Horcruxes were still intact. It cost him his own sense left - smell - and his nose died, rotted and fell off ... unless he cut it off himself."