Here are some rules for behaviour in, and outside, the jungle.

Do not feed the animals

In particular, do not feed monkeys, orangutans, gibbons and other primates.

Reasons: 

• Primates are genetically closely related to humans (and therefore susceptible to most human illnesses), but have little or no resistance to our diseases. Food touched by humans can carry bacteria, and close exposure to primates, when feeding, can allow viruses to transfer from human to animal. Infant orangutans, with weakened immune systems are particularly vulnerable, and indeed the orangutan infant mortality rate at Bukit Lawang is several times higher than the natural rate - feeding orangutans kills them.
• Bukit Lawang's primates, are almost entirely arboreal (tree-living). This is a lifestyle evolved over millions of years, keeping them safe from predators on the ground. By feeding them, you change their behaviour bringing them down to the forest floor, where they are more vulnerable to predators.
• Primates play an important role within the ecosystem for seed dispersal - fruit are eaten and their seeds discarded or excreted by the primate. If primates no longer seek food from trees, instead preferring human food, they will no longer perform this role.
• Primates (orangutans, macaques) that become accustomed to being fed by humans may become aggressive in demanding food from humans. This is dangerous for the animal (if the animal is injured during a confrontation with a human), and for humans who are at risk of serious injury and disease from primate attacks. Mina, an orangutan in Bukit Lawang, has attacked or pursued humans on numerous occasions, in search of food.
• Feeding monkeys can disrupt their troop, resulting in excessive numbers and therefore increased intra-troop violence.

Do not leave rubbish in the jungle

Rubbish is unsightly and unhygienic. Plastic waste is a choking hazard for animals. Cigarette butts are plastic, and take many years to decompose. 

Food waste, such as fruit skins, is likely to be consumed by animals, and is a source of disease for them, so it should be packed and brought out of the jungle.

Do not go into the jungle if you are sick

• As mentioned above, wild animals are highly vulnerable to human illnesses, and if you go into the jungle while ill, then you are more likely to spread your illness to them. 
• Jungle trekking is a strenuous physical activity, and trekking while ill is unfair to other guests and your guide, and may aggravate your illness.

Do not approach animals too closely

Keep at least ten metres from wild animals. Airborne transmission of viruses from humans to orangutans is more likely the closer you approach. Feeding animals causes them to come down from trees, greatly increasing their proximity to humans.

Obey appropriate toilet/hygiene rules

• Carry alcohol hand gel to disinfect your hands after you go to the toilet, to avoid spreading bacteria.
• If you need to go to the toilet, you should bury any solid waste, and you should not defecate in areas frequented by orangutans.
• Do not pollute rivers with soap or shampoo - it upsets the chemical balance of the water and kill organisms in the water, and also cause algae blooms.