Tales From the Sock Drawer: The Shampoo O' Plenty

Not all the things in my sock drawer are creatures.  Some are inanimate objects.  Take for example my magic shampoo.  I've been washing my hair with the same bottle since the summer of 2009.  That's three whole years!  And it's not like I skimp on the stuff, yet whenever I pick it up it always manages to remain about one third full.

I've asked my pharmacist for his take and he has no explanation.  Me, I'm beginning to wonder if it has a wormhole inside it connected to a giant shampoo vat.  Either that, or I happened to pick up some kind of magical shampoo o' plenty.  I suppose its possible somebody is playing a trick on me, and pouring some back in when I'm not watching, but that would just be weird.