The rosewood tree is one of the most trafficked species on earth. When it's cut it bleeds a blood-red sap. Having exhausted stocks elsewhere, Chinese traders have turned to West Africa, especially southern Senegal, where trees are cut down and smuggled into neighbouring Gambia and then all the way onto China. For a year BBC Africa Eye, with Umaru Fofana, has been investigating the million-dollar trade in trafficked rosewood.