The Skin I Live In

Plastic surgeon Robert Ledgard was successful in cultivating an artificial skin resistant to burns and insect bites, which he calls "GAL", that he says he has been testing on athymic mice. He presents his results in a medical symposium but when he privately discloses he has also conducted illegal transgenic experiments on humans, he is forbidden to continue with his research.
On his secluded estate, Ledgard is keeping a young woman named Vera captive, with the help of one of his servants, Marilia. Due to the suspension of his official experiments, Robert asks Marilia to dismiss the other servants.
While Robert is out, Marilia's son Zeca, having committed a robbery, arrives and asks his mother to hide him for a few days. He sees Vera on Ledgard's security camera screens and demands to see her in person. When Marilia refuses to let him stay after she invites him in, he binds and gags her and then rapes Vera. Robert arrives and kills Zeca.
While Robert disposes of Zecaâs body, Marilia tells Vera that she is the mother of both Zeca and Robert by different men, a fact she has not shared with them. Robert was adopted by Mariliaâs employers but was ultimately raised by her. Zeca later left to live in the streets and smuggle drugs, while Robert went to medical school and married a woman named Gal. When Zeca came back years later, he and Gal ran off together. They were involved in a terrible car crash in which Gal was badly burnt. Thereafter she lived in total darkness without any mirrors. One day, while hearing her daughter Norma singing in the garden, Gal accidentally saw her own reflection in the window; traumatized by the sight, she jumped to her death.
In the present, Robert returns and spends the night with Vera. During the night, he dreams of his past, specifically the night of a wedding six years earlier, where he finds Norma (his daughter) unconscious on the ground. Norma, who had been taking medication for psychosis, comes to believe that her father raped her; she develops a fear of all men and spends eight years in a mental health facility. She eventually kills herself in the same manner that her mother did.
Vera, too, dreams about the same event: Vicente, a young man who works in his mother's dress shop, crashes the wedding and meets Norma. Like others at the party, he is under the influence of drugs. He walks with Norma into the garden. Norma begins to take off some of her clothes, stating she would be naked all the time if she could. Vicente kisses her and compliments her. While they are lying down with Vicente on top of her, she suddenly starts repeating "no, no, no" and begins screaming. She bites his hand. Surprised, he slaps her, knocking her unconscious. He flees the scene, confused and nervous, just before Robert arrives.
Robert tracks down Vicente, kidnaps him, and subjects him to sex reassignment surgery. Over a period of six years, Robert physically transforms Vicente into a replica of his late wife, and calls him Vera. During this period of time, Vicente struggles to keep himself sane and cling to the core of his true identity.
After an absence of four years, Marilia returns to work in Robertâs house to look after Vera (Vincent). Vera reveals to Marilia that he has been held captive for the last six years.
Back in the present, Robert's new relationship with Vera dismays Marilia, who does not trust Vera. Fulgencio, one of Robert's colleagues, reads a news story about the missing Vicente and recognizes him as one of their sex change patients. He accuses Robert of falsifying Vicente's consent and of experimenting on him. Vera arrives to support Robert, asserting his willing participation. During the night, Robert and Vera try to have sex, but Vera tells him that he is still sore from being raped. Ostensibly going downstairs to find lubricant, he retrieves Robert's gun and kills Robert and Marilia.
Freed from captivity and the need to play along with Robert's whims, Vicente (Vera) returns to his mother's dress shop for the first time since his kidnapping. He tearfully tells his lesbian ex-colleague Cristina (whom Vicente had loved six years prior) of his kidnapping, forced sex change, and the murders. Then, as his mother enters the room, Vicente quietly reveals his identity to her in the final line of the movie -- "I am Vicente."

Question: What did Norma do to Vincente's hand?
Answer: bit it