In February 2020, a shocking video began to circulate on Chinese social media. A group of African children are being instructed, by a voice off-camera, to chant phrases in Chinese. The kids repeat the words with smiles and enthusiasm - but they don't understand that what they're being told to say is "I am a black monster and my IQ is low." The clip ignited outrage in China and beyond. But no-one ever answered the crucial questions: Why was this filmed? Where was it shot? Who made it? These questions send #BBCAfricaEye and #BBCEyeInvestigations reporters Runako Celina and Henry Mhango on a journey into a Chinese video-making industry that exploits vulnerable children across the continent.