The Predator film provided a variety of hardships for the actors, such as leeches, snakes, stifling humidity, heat and rough terrain. All of the night scenes were filmed during freezing-cold temperatures, which was especially hard on Arnold Schwarzenegger during the latter half of the film when the mud he had to wear (actually pottery clay) became cold and wet.
He was warned it would take his body temperature down a few degrees and he shivered non-stop, even when they tried to heat him with lamps (it just made the clay dry out).

The Yautja, known colloquially as the Predators or Hunters, are an extraterrestrial species characterized by their hunting of other dangerous species for sport and honor, including humans. They were also referred to once as Xenopredators. The Yautja are a sentient, humanoid race that breathe an atmosphere similar to that of Earth's, but possess a level of technological advancement far in excess of anything available to humans.