The range increments. Corrosive Spit range increments are [Body] meters. Elemental Attack is [Magic] meters. In addition, Corrosive Spit causes Acid Damage, whereas Elemental Attack can be Acid, Cold, Electricity, Water, or Fire. It's really a matter of trappings (if I may use a Savage Worlds term). The Corrosive Spit is a physical ability whereas the Elemental Attack is magical in nature.