The vampire sinks those pointy teeth in that attractive neck, the victim sinks helplessly to the ground - and then rises as a vampire! Every night this happens.
Yeah. So why isn't the world clogged with vampires?
Think about it. Say there's only one vampire. That one vampire drinks and makes a new vampire tonight. So tomorrow night there are two hunters stalking the night.
Those two drink and then there are four. The next night eight. Multiply that by 2 and you get 16, then 32, then 64…
If you're a math geek like me, you know that the equation for that is two to the power of however many nights have passed. Otherwise, you might pull out a cheap calculator and keep multiplying by two. Do that just 30 times, one average month and you know how many vampires you have?
That's over a billion vampires in one lousy month. The earth would be overrun!
There are two ways a writer of vampire stories can deal with this problem.
First, set a rule that a vampire doesn't create a new vampire every time they drink. They have to go through a special process called "siring" or something. Some fine stories have been told along that line: Buffy the Vampire Slayer is my favorite.
But the other way is to embrace the problem. What if the world was so clogged with vampires that they filled every nighttime street, crowded every window so you couldn't see out of your house?
But only at nighttime. And they can't come into your house unless you invite them.
Could you still order a pizza? Could you still work a job? If your bus breaks down on the way home, what then?
Lots of possibilities for stories…