Each grey disc is a red blood cell flowing through the Remoscope. A Plasmodium falciparum parasite lives inside a red cell and shows up as a small dark ring, blob or cluster. Three forms, youngest to oldest:
Controls. Click a parasite to mark it (+points, more for rings — they are the hardest). Wrong click: −25. If you think the frame is clean press N / No parasites. Press Enter / Done when you have found them all. Miss any and you lose a life.