The world is very worried about coronavirus variants. As the virus mutates — which all viruses do — variant strains emerge. Some of these variants are more effective at infecting humans and may even cause more severe disease. Variants that appear to fall into this category have been identified in Brazil, South Africa, the United Kingdom — and now India. And in an interconnected world, they can spread from one country to another. How does a mutated version of the virus improve its chances of being transmitted to humans? If you imagine viruses as puzzle pieces, as this video does, that can help explain what is happening when a coronavirus variant comes into contact with human cells.