Marjorie Castro, head of the zoo, said one of the zoo's five gorillas threw a stone measuring about 2 inches in diameter Saturday and the rock struck a 38-year-old woman in the forehead, Swedish news agency TT reported Monday.
"At first everything seemed fine. She was bleeding a little from her forehead, but seemed to be in good health," Castro told the Aftonbladet newspaper. "But she was hit in the head and gorillas have enormous strength, so we called an ambulance. After a while, she felt weak and we had to lie her down."
Castro said the incident marked the first time the zoo's gorillas had thrown anything besides grass at visitors.
However, some zoo visitors said otherwise, including a mother who said a gorilla threw a rock at her 7-year-old son in July.