So sometimes you're just sitting there, reading a book or typing at your PC, and you notice this vague itch on your arm, leg or wherever. The odd thing about the itch is that it's on the move.
You inspect the area closely, and notice some little thing with 6 or 8 legs trying to go about its daily
business in the relatively futile environment that is you.
Now, if you're not the kind of person who goes "urgh" and brushes it off, you'll take pleasure in watching the little guy explore the treacherous heights of your arm hairs and the dark oases of your moles. And quite often, especially if you're ignorant of these things like me, you'll find yourself wondering, what the hell is this little bugger? What does it do when it doesn't get side-tracked marching around on you?
So you go to this website (bugfinder.com is already taken by C++ programmers), where it asks you a series of questions which are based on a decision tree structure. Things like "how many legs does it have?" and "did it drop off your head when you were combing your hair?"
You answer however many questions it takes to uniquely identify your insect/spider/whatever, and then it tells you about it, pictures and all. Then next time you find one looking lost and confused near your elbow, not only will you recognise it, but you might even be able to point it in the right direction (the creature, not the elbow).