Reported incidents of these sorts of monsters vary somewhat, but there are several basic characteristics that pop up over and over again. In most cases, the eyewitnesses describe a beast that is 4.5 to 5.5 feet (137 to 168 cm) tall, with an oval-shaped head bearing glowing eyes with an alien-like shape. Most descriptions claim that the creature has long, sharp spines that run from the back of its head down the spine, ending at the rump.

Many eyewitnesses report a strong, unpleasant, sulfur-type odor, but others say that the creature has no smell. Some say the skin is similar to a frog’s — green in color with mottled specks; others claim that it has the appearance of furry lizard with scaly skin.

Although the bipedal creature generally ambles on two legs, it has been known to run on all four. Many assert kangaroo-like qualities, saying that the Chupacabra uses its strong hind legs to jump rather than walk. Others suggest a more ape-like quality to the creature’s gait.

The origins of the Chupacabra are a subject of debate, as well. Some people believe that this creature is the left-behind pet of visitors from outer space — hence their uncanny resemblance to space aliens known as “grays.” Both reportedly have large, oval heads with enormous eyes.

The alien theory doesn’t end there, however. Others speculate an alien-animal crossbreed created by scientists at NASA, suggesting that the creatures are escaped experiments gone awry. One veterinarian in South America believes that the Chupacabra is a genetically modified vampire bat. Other medical and official personnel suspect that these incidents are caused by packs of wild dogs.

Whatever the case, it’s interesting to witness people’s reactions to phenomena like this. People are particularly interested in the Chupacabra for the same reason they are fascinated by humanoid extraterrestrials: We are drawn to the idea of human-like creatures, with human-like intelligence, because it means that we are not alone in the universe.