The following article lists what is known of Melmacian physiology:
Melmacians have only four teeth, making Melmacian dentistry a rather simple career choice.
Melmacians have eight stomachs, comprising 8 of their ten major organs. The Melmacian liver is located behind three of them. Some of the stomachs are spare and open up when depressed, increasing appetite.
The Melmacian heart is in the head.
The Melmacian reproductive organs are apparently below the waist as ALF on more than one occasion tells people not to touch him below the belt.
Melmacians are capable of hearing higher frequencies of sounds than humans. ALF is able to hear dog whistles.
Normal oral temperature for a Melmacian is stated as being 425 degrees and 114.8 degrees on different episodes. The latter temperature makes more logical sense, as 425 degrees Fahrenheit would mean that his internal organs would be constantly baking (although this could explain why Melmacians can metabolize such large amounts of food).
In addition to bi-monthly feeding frenzies, Melmacians also go through a 12-hour phase once every 75 years in which their insticts kick in and they must hunt for cats. During this time they will attempt all sorts of deceptions in order to eat a cat. For ALF, this occurs on March 2 every 75 years.
Known Melmacian ailments include the dreaded Melmacian hiccups.
Melmacians were immune to infectious diseases because of the immunity bolstering properties of the Carl Shrub in their diets.
Melmacians die at age 650. The week before they die, they give away all of their possessions. The year before they die, their credit cards are cancelled.
Earth cotton is an addictive substance for Melmacians. ALF goes through a period of addiction in which he tries to move to Alabama.