This video compares 1918 flue H1N1 to the current threat: avian flu H5N1. Using animation, the video explains (1) the mechanism of how viruses enter target cells and release from target cells, (2) why 1918 flu named H1N1 and avian flu named H5N1, and (3) why viruses that transmitted only bird-bird can gain the ability of bird-human or even human-human transmit. Biotechnologies such as reverse genetics and electron microscopy are shown. In this webpage "Reviving the Virus" lead readers to a series of arguments and counterarguments of whether deadly virus should be revived for research purposes. Students not only have the opportunity to justify their own stands, but also examine the other viewpoints. Teachers' guide is available from this website http://www.pbs.org/wgbh/nova/teachers/programs/3318_02_nsn.html. Check the following website for avian flu http://www.pbs.org/wgbh/nova/sciencenow/3302/04.html