Brain capacities generally are reported to be double that of humans in comparison to body size. Brain structure is reported to be three-lobed, somewhat between human and dolphin. Large frontal lobes connect expanded visual areas to the oversized, almond eyes. Some greys have mutliple inner eyelids. Digestive systems are reported as atrophied in comaprison to human digestion.
Nutrition appears to be absorbed dermally, or possibly directly injected.
It is commonly reported that the greys either soak themselves in a slurry solution, or enzymatic bath, or smear a peroxidated nutritional solution on their skin. This would explain their strange bodily odor, which has been described variously as like burnt wood, cinnamony, mentholated, or an electric-ozone smell. Skeletal structure is child-like, with spindly limbs generally elongated beyond human proportions. Genitalia also are reported as child-like or absent, in the case of the clone class. Some greys appear to be genetically engineered replicants, with minimal internal organs.