You're more than a little sure this guy is just a crazy hobo when you look at what he's offering you - a Barry Goldwater campaign pin, a shard of a 45 you think is "Penny Lane/Strawberry Fields Forever," the POKEY chip from an old Atari home computer...a lot of junk, mostly. But the easiest way to deal with people like this is to play along, so you grab an item at random, thank him profusely, and saunter off. Once you're some distance away, you stop to look at what you grabbed. It's a...well, you honestly have no idea what it's supposed to be. It's pink, and it's shaped like a wolf's paw print (thank you, 6th grade biology,) but it's not rubber, so it's not an eraser, and it's too light to be a paperweight...What a piece of crud, you think, as you fling it into the trees and walk on.
A little ways down the path, you are suddenly siezed by an intense, full-body itch, the likes of which you've never felt before. Social conventions be damned, you rip your clothes off; this is so in need of immediate attention that you wouldn't care even if there were people around. The last piece of clothing falls to the ground...
...and you're just in time to watch brown fur begin to grow from every follicle on your body, except from your chest down to your groin, which is white. It stays pretty short, and the itch subsides as quickly as it came, but the weird stuff has just begun.
Your body gets slimmer and stronger, though not visibly muscled. Your face pushes outward, forming into something closely resembling a wolf's muzzle, but with enough human attributes remaining to be recognizably the face of an intelligent creature. You notice yoiur clothes unravelling for no discernible reason as your ears become thin and triangular, moving to the top of your head. Your legs change, reproportioning themselves and becoming double-jointed, leaving you able to move bipedally or quadripetally equally well, your feet becoming wolf's paws. Your arms also reproportion, but you hands stay hands, though they gain the pads that your feet already have, and the fingernails become claws instead. There's a pressure at the base of your spine, which suddenly extends into a beautiful tail. You're now an anthropomorphic wolf. It seems that your changes are over...
...but they're not, not quite. Your hair changes to a darker shade of brown than your fur and grows about halway down your back. Your formerly ramrod-straight figure becomes soft and curvy, flesh massing underneath your nipples, expanding into two nice-sized breasts, a thin layer of muscle forming underneath the skin to support them, a sort of natural brassiere. And finally, your privates change, leaving you completely female.
You don't have a mirror handy, but you don't need one to realize what's happened - you've become an anthro wolf-girl, naked, all alone in the woods...
But on the other hand, you think, looking at your new claws, if the woods decide to try anything, I'm ready for 'em.