Using Legos and toy soldiers, UT-Austin biologist Chris Sullivan explains the concept of viral latency, which is a mechanism that certain viruses, including herpes and HIV, have evolved to hide from the host immune response. It's this ability to hide away in a "latent reservoir" that makes it impossible to cure these diseases. 

Read more about how Sullivan is working to "trick" viruses into exposing themselves while latent, which could enable a true cure: web5.cns.utexas.edu/news/2012/12/biologist-eradicating-latent-viruses