why some people have green blood?

Sulfhemoglobinemia is a condition where a person develops green blood.                                                                                                     In 2007 , surgeons operating on a 42 year old Canadian man got a shock when they discovered dark-green blood causing through his arteries.                                                                                                                     Stunned, the medical team immediately sent his blood for analysis the test revealed the blood discoloration was caused by sulfhemoglobinemia which occurs when a sulphur atom gets incorporated into the oxygen-carrying haemoglobin protein in blood.