International Expeditions’ naturalist-guided Amazon voyages give you the chance to spot some of the thousands of species of animals that live in the rainforest. While some move so fast you may only catch a quick glimpse, you'll likely have plenty of time to observe a sloth. These gentle creatures are never in a hurry and spend much of their time languidly napping or eating in the trees of the Amazon rainforest. They are not just slow-moving, but in fact sloths are classified as the slowest animals in the world.

There are five known species of sloths divided into two families depending on whether they have two or three toes, but they are all arboreal and hardly ever leave the safety of the trees. They even mate and give birth while hanging from branches.

Sloths typically spend their time alone not making a sound, but when it comes time to mate, the female will utter a high-pitched cry to beckon a male to her side. After six months to a year, a newborn sloth enters the world. Babies get a free ride on their mothers' stomachs until they are between nine months and two years old, depending on the species. At this time, they set out on their own.

Scientists believe the reason these animals do not move very quickly is for protection and defense. Instead of running at the threat of danger, the sloths simply don't move. Their thick, bristly fur helps them blend in rather well with their surroundings, and there may be algae growing on a sloth's coat that gives it a greenish hue.

So if you think you saw a clump of plants rusting in the trees, be sure to take a closer look, as there may be a sloth nestled in the branches overhead. They sleep anywhere from 15 to 20 hours each day, but even when they are awake, you might not see them move. While they are likely alive and well, their long claws are able to grip the branches with such strength, they often remain in their position even after they die.