It was the third time in the last month that canines have been seen in Mexico trotting off with human body parts.Police in the southern state of Oaxaca said they responded to a call Wednesday morning about "a black dog that carried in its mouth a human arm."In early November, clandestine graves holding human remains were found in the central Mexican state of Guanajuato, after neighbors reported to volunteer searchers that they had seen a dog with a human leg.Drug cartels in Mexico frequently leave notes alongside heaps of dismembered human remains, as a way to intimidate rivals or authorities.In June, the bodies of seven men were found in a popular tourist region with warning messages written on their corpses referencing the Gulf Cartel, which operates mainly along the U.S. border to the north."