Final answer:
Persephone spends 1/3 of every year with her husband in the underworld because she ate pomegranate seeds while she was there.
Step-by-step explanation:
Persephone spends 1/3 of every year with her husband in the underworld because of a small slip-up. In Greek mythology, it is believed that Persephone ate a few pomegranate seeds while in the underworld, which bound her to stay there for a portion of the year. Hades, the god of the underworld, had tricked her into eating the seeds, resulting in her having to spend a certain period of time with him.