Just a little oddity...posting here because it leans toward the horticulturally-minded.
My son has his own bit of garden to do whatever he likes with - which normally involves growing massive sunflowers for some reason. He has a bird table next to it, which he fills regularly and watches from his window.
Birds have no manners, and tend to spill as much as they manage to eat, so his patch gets all sorts of odd stuff growing in it. I was weeding inbetween the sunflower forest, pulling up anything that wasn't obviously a sunflower, and I pulled up a plant about a metre high which I recognised as the species cannabis sativa.
I guess it must have come from the bird seed, unless there's something my six-year-old isn't telling me...
I always thought that hemp seed was sterilised so it wouldn't grow, but I guess not. So there's a tip for all you would-be drug barons out there - don't waste your money on seeds from Africa - wild bird food only 3 quid for a 2k bag!!