There is a water processing plant located along the trail from MacRitchie Reservoir to Bukit Timah Hill (this overlaps with the latest rainforest canopy walk trail). Do not take photos of this water processing plant or else the guards will shout at you and give you warning. This is because they are afraid of terrorist attack on this facility, so do take note.
You will encounter monkeys while exploring the MacRitchie, Seletar and Pierce areas. Remember not to feed the monkeys and always keep an eye on your belongings. The monkeys are very fast and may snatch your belongings away from you. Some can be very agressive so be careful.
You may encounter snakes, monitor lizards and other animals in the rainforest trails. Do not panic when you encounter them. Stay calm and let them move past you. Remember that they are more frightened by you then you are frightened of them because you are much bigger and they may think you are a predator.