Bones of their prey is a source of calcium for snakes, and monitors, as well as other herps. Vegetarians, such as the Green Iguana need sunlight (UVA/UVB) so that they can produce D3. When Iguana's don't get enough calcium, such as D3, their bodies begin to absorb it from their bones, which causes weird warps, kinks, fragile/glass bones etc...number one cause of MBD...and the number one killer in Iguanas.