Don't throw foreign objects in the animals' exhibits," guards stationed at several locations around the Jerusalem Biblical Zoo constantly warn visitors. The fact that many zoo visitors disregard this warning led to the untimely death of an innocent Jerusalem hippopotamus. When the Jerusalem Biblical Zoo moved from Romema to Malha in 1993, Matti the hippopotamus was separated from his interspecies love, an elephant friend that moved to the Safari Park in Ramat Gan. But Matti soon found solace in a more "suitable" partner - Tami the hippopotamus. Their tragic love story ended last week when Matti, 30, was found dead in the hippopotamus pool. Although he looked sick prior to his death, zookeeper Gilad Moshe, 26, said he was not sure how to help the hippo, and Matti's size prevented them from taking x-rays. "He looked swollen and bad, and he wasn't leaving the pool," says Moshe, who has worked at the zoo for 12 years and with Matti for the past six months. Hippopotami have a general dislike of the sun and tend to spend most of the day in the water. Moshe says Tami and Matti usually stayed in the water until at least 5 p.m. every day. Nonetheless, Moshe could tell his behavior was uncharacteristic. Matti was given an antibiotic injection, but unfortunately it was not until Matti's passing that the true cause of death - a tennis ball that found its way into Matti's exhibit area - was determined. "After he died we opened him up and found the tennis ball," Moshe told In Jerusalem. Matti probably ate the tennis ball thinking it was an apple or another piece of food from his normal feedings, he explains. According to Moshe it is a "miracle" that incidents like this do not happen more often. He finds all types of foreign objects littering the exhibits at the end of the day, including "bottles, plastic bags, and even knives and kids' shoes." The saddest part about Matti's death was watching Tami's reaction, Moshe says. She is eating less, and when Moshe went to feed her, she just looked at him open-mouthed. When the zoo workers emptied the pool to remove Matti's body, Tami tried to lick him and nudge him to move. Although Moshe ultimately holds the zoo staff responsible for not finding the ball in time, he wishes people would take warnings more seriously. Zoo officials regularly educate people about why feeding animals and throwing things in their living space can be dangerous, but not everyone listens. During Pessah, many zoos in Israel passed out leaflets to every visitor asking them to protect the health of animals and the cleanliness of exhibits. Zoo officials also ask people to tell zookeepers when they spot plastic bags or other objects that could harm animals. More than 70 guards supervised the the exhibits during the holiday, making sure people refrained from throwing objects at the animals. How did the ball end up in Matti's exhibit? "Your guess is as good as mine," says zoo director-general Shai Doron. It could have been a child playing with a ball that rolled down the hill toward the hippos, which live in one of the lowest points of the zoo. Yet Doron insists zoo behavior has improved significantly in 13 years since the new zoo opened. Aliza Roman, section head of the small animal building, says she feels very lucky most of her animals are protected by glass. But that does not mean they cannot be harmed by visitors. "Snakes are very sensitive to vibrations, so when people knock on windows or glass it is upsetting to the animals," Roman says. People do not always mean to hurt or bother the animals - it is a means of communication with the animals. Some people put all their aggression into banging on the glass, she said. "It's upsetting and a little scary [when] it's a poisonous snake. What if they did break the glass," she asks - even though she luckily doubts that this could happen. Roman is also in charge of the outdoor lemur exhibit, where she often finds objects such as gum, coins, wrappers, ice cream sticks and sticks with points to prick the lemurs. "I am so lucky the lemurs don't touch the stuff people throw in. It's as if they want to kill the animals," she says. Animal feeding is another common problem. Jerusalem zoo animals share the local love for Bamba. Unfortunately, however, animals cannot digest the peanut butter puff like humans. The monkeys get diarrhea and then they cannot eat their regular food. "They eat the Bamba and they pay for it days later with a special diet," she says. On one previous occasion, the recklessness of a visitor also led to the death of an animal. A toco toucan was found dead in its cage on June 1, 1997, with bits of avocado around it, says Beverly Burge, section head of the hospital quarantine unit. Along with chocolate, avocado is a known bird toxin and, in fact, the autopsy report showed an increase in toxicity level for the bird. People respond to explanation and education, rather than warnings and admonition, says marketing and public relations director Sigalit Dvir. "It doesn't work to shout because people are here to enjoy themselves. We explain the diet, needs of the animal and why throwing things in the exhibit is bad," she says. Recently Roman saw a child playing with a small ball and asked the child to put the ball away. The mother defended her child, claiming it was "just a small ball." "You know a small ball killed our hippo," Roman replied. The mother quickly apologized and put the ball away. Matti's death drew criticism from groups such as Israel's Anonymous for Animal Rights. "Animals are not for entertainment, and when you use them for entertainment, people will do things like throw a tennis ball to a hippo," insists Anonymous manager Menashe Eliezer. People for the Ethical Treatment of Animals (PETA) says on its Web site, "Zoos teach people that it is acceptable to interfere with animals and keep them locked up in captivity where they are bored, cramped and lonely. Zoos claim to educate people and preserve species, but they usually fall short on both counts." But director-general Doron disagrees with PETA's account of zoos. "The model of zoos today are one of the most important concepts for conservation," he says. Zoos have become conservation centers for endangered species or rare animals. The Jerusalem Biblical Zoo is involved in a reintroduction project of deer into the Jerusalem Hills. The zoo has almost 600,000 visitors a year and for many it is their only chance to learn about wildlife and conservation. "Education is the basis for a better world concerning environmental issues and wildlife conservation," he says. Until the world solves endangered species and conservation problems, zoos may be the only answer. "In a perfect world there would be no zoos," Roman says. "We would be together with the animals like Adam and Eve in Paradise."