Flu Attack! How A Virus Invades Your Body

This is a pretty nice animation. I did cringe though when he said that 'all viruses want to spread'. In terms of natural selection it is much better to think of selection as favoring those viruses that spread most successfully therefore favoring those that spread most efficiently. They've also made a very clear decision to avoid virtually all terminology and use familiar terms (locks, keys, noodly things, factories, copying machines, little chefs).

Notice all the antibodies swirling around the virus at the very end. It is the fact that these antibodies latch onto the virus (via the same lock and key mechanism) that marks the virus for destruction via the white blood cells (actual white blood cells may not actually make a slurping noise).

The answer to the final question - of why you don't usually drop dead is also rather weak. The fact you have so many cells won't keep you alive for long if a virus multiplied this fast. They actually have a better answer at the NPR website:

In our video we ask, if a flu virus inside your body can multiply by the millions within seconds, why don't we topple over and die quickly?

Here's a better, longer answer than the one in the video. First, some new viruses get caught in mucus and other fluids inside your body and are destroyed. Other viruses get expelled in coughs and sneezes. Second, lots of those new viruses are lemons. They don't work that well. Some don't have the right "keys" to invade healthy cells so they can't spread the infection. And third, as the animation shows, your immune system is busy attacking the viruses whenever and wherever possible.