S1·E2 The Sohma Curse

Tohru is quite surprised to see Yuki, Shigure, and Kyo turn into animals. While still in their animal forms, they tell her about the Sohma Family Curse. Whenever a member of the Sohma family is hugged by a member of the opposite sex, they turn into animals from the Chinese Zodiac. Later on at school, Yuki confronts Tohru and tells her that her memory may have to be erased because she found out the family secret. When they return home, Shigure informs them of Akito's decision: Tohru can stay at the house and won't have her memories erased as long as she doesn't tell anybody about the family secret.