I was thinking, as I sometimes do, about the nature of "kidding." Often, when one wants to say something cruel or socially unacceptable they cloak it in a "joke," and that makes it OK. Clowns operate in that way. Viruses do, too.
Viruses can only pass through the body's defenses by wearing a protein coat (or something like that). It fools the body into thinking, "Oh, this guy's OK. He's just a plain ol' protein thingy." Then, when the little bastard gets in, it delivers its payload and WHAM! You're in big trouble.
That's all I have to say, dummy. Just kidding! Ha Ha! I was only joking when I called you a dummy! Have a good laugh at your own expense, buddy!