In the "D&D" universe, there are many different species of dragons. However, despite their variety, a number of traits are common to nearly all types of dragons. All species appear to be generally reptilian or serpentine in their natural form. Except for the youngest dragons, they tend to be quite large—usually at least as big as a horse, and often much larger. Most species depicted have wings and are able to fly, and nearly all are quadrupedal. Almost all species of dragon are highly intelligent (at least as intelligent as a human being) and are able to speak. Essentially all species of dragon are said to be magical in nature, and in most species this nature is expressed as an affinity for some type of elemental power; some dragon species are naturally able to cast magical spells, as well. Most dragons have the ability to breathe or expel one or more types of energy associated with their elemental affinity, as well as bearing some resistance to damage or injury from any other sources of such energy. Dragons are egg-layers, and most have sharp teeth, horns, and claws. A "D&D" dragon is protected by its scaly hide, the color of which is determined by the dragon's species, and which also offers a visual clue to the specific elemental nature of each species of dragon. Each species of dragon has a particular temperament associated with it, as well as a deeply rooted moral outlook derived from that temperament; these factors underlie the personality and behavior of each individual dragon. Typically, dragons do not vary widely in appearance or personality within a species, although exceptions are possible, especially in certain "D&D" settings, such as Eberron.