Five Shocking Zoo Attacks Zoos: They're supposed to be places of fun and learning, where curious animal admirers can observe an array of fascinating creatures at a safe distance under controlled conditions. But sometimes, even at zoos, when humans get too close, tragedy can strike. Learn more tonight on "20/20: When Animals Strike Back" at 10 p.m. ET and click through to read about five unbelievable animal attacks at zoos around the world. Berlin Zoo, 2009, Polar Bear On April 13, 2009, a woman jumped a fence at the Berlin Zoo, entering the polar bear enclosure during feeding time. After thrashing in the enclosure's moat with a bear biting her back, the woman was pulled to safety and treated for severe injuries. A video of the incident shows the woman in the moat attempting to grab life preservers and ropes thrown by would-be rescuers while one of the bears repeatedly bites her rear end. At one point the rescuers managed to lift the woman out of the water, but only seconds later she fell back in and was again attacked by the bear. When rescuers were finally able to pull the woman out of the bears' moat, she was taken to a nearby hospital, police said. "What she's done here, she should thank the good Lord she's alive," Jack Hanna, director emeritus at the Columbus Zoo in Ohio, told "Good Morning America." "Maybe they were already fed and wanted to bat her around some, because let me tell you something, that polar bear, in one split second she would've been history," Hanna said. Police did not know why the woman jumped the fence into the enclosure, but they did issue her a citation for trespassing. Watch the full story on "When Animals Strike Back" on "20/20" Friday at 10 p.m. Singapore Zoo, 2008, White Tigers In 2008 at the Singapore Zoo, three white Bengal tigers mauled a zoo cleaner to death after the man walked through a moat surrounding their enclosure, the AP reported. Amateur video shot by a zoo visitor shows a man, holding a broom and a plastic yellow bucket, wading purposefully across the moat toward the tigers' habitat. His arms spread wide, he does not resist as a tiger claws his chest and bites his neck. Another tiger joins the first in nuzzling the man, who by this point seems to be shouting. After the tigers start to attack, he puts the bucket over his head. "Get in the water!" a visitor repeatedly shouts. The attack proceeds. A zoo official told the AP the man was Nordin bin Mondong, a 32-year-old Malaysian. Zoo workers eventually distracted the tigers and pulled Nordin away, but he died on the way to a hospital, the official reportedly said. The official did not say why Nordin may have jumped into the tigers' area, the AP reported. San Francisco Zoo, 2007, Tiger On Christmas Day, 2007, a 350-pound Siberian tiger named Tatiana managed to escape its cage. The tiger mauled three men, killing one. Seventeen-year-old Carlos Sousa Jr., of San Jose, Calif., was killed. The other two had surgery to treat their wounds. Authorities were unsure of how the tiger escaped, but it was clear that somehow the animal traveled over a 20-foot wall and a 15-foot moat. Initially, authorities worried that four of the zoo's five tigers had escaped. Later they learned Tatiana was the only one loose. Police were unsure how long the tiger roamed free at the zoo, which is open 365 days a year. Between 20 and 25 people were on site when the attacks happened, according to the AP. Employees and visitors were told to take shelter when zoo officials learned of the attacks. When police arrived, they found Tatiana sitting beside one of the surviving victims near the zoo's cafe. When it moved toward officers, they opened fire and killed the tiger. The event marked the second time Tatiana had mauled someone. On Dec. 22, 2006, the tiger attacked a zoo keeper during a routine public feeding. It reached through its cage, grabbed the zookeeper and tore flesh off her arm. Copenhagen Zoo, 2012, Siberian tiger Just last week, a 21-year-old man was killed after he entered the Siberian tiger den at the Copenhagen Zoo, in Denmark, the AP reported. On July 11, an Afghan-born Danish citizen entered the den and suffered bites to the throat, face, chest and thigh, police told the AP. They didn't know how or why he entered the den, and suicide was a possibility, the report said. "He has been in the water and the animals must have seen that and attacked him," a police spokesman told the AP. It was the first such incident in the 152-year history of the zoo, and the zoo didn't plan to kill the tigers, the A.P. said. Anchorage (Alaska) Zoo, 1994, Polar Bear In July 1994, a 29-year-old Australian tourist named Kathryn Warburton climbed a fence and railing to get close-up pictures of a polar bear named Binky at the Anchorage Zoo, the AP reported. Warburton survived the attack with a broken leg and bite wounds, the report said. Binky kept Warburton's shoe for three days before it was taken away by zoo staff, the Anchorage Daily News said. The paper later reported that Warburton blamed herself and quoted her as saying, "It was the dumbest thing I've ever done."