This is an old one, but a great one. Apparently in some places in South London (Brixton), New York, Chicago, anywhere where drugs is a bit of a problem, there are these squirrels that have become unusually aggressive in their search for drugs - having become, as it were, addicted to crack. Or, as I like to say, crack-addled squirrels.
Now there's more than a slight whiff of Urban Legend to this one, but it's been so widely reported that one can't held thinking that maybe, just maybe there's a slight grain of truth to it...but..., well, it's the media after all. Read with caution.
Links: The Sun (UK) - Squirrels go nuts on crack, The Guardian, The NY Times, Various YouTube videos on the Crack Squirrel Problem, Christine O'keefe Aptowicz performs Crack Squirrels, and finally, a seemingly irrelevant connection to Russia where they don't seem to have made the connection - Russian Squirrel Pack Kills Dog.
I couldn't make this stuff up.