Sook-Yin Lee advises Dandyhorse (Summer 2009, not onliné) how she gets motorists the fuck out of her way:
Though I love ringing my bell, more often I use my high-pitch falsetto voice to tell cars I’m coming through. I let out one long, high-pitched, paint-peeling DOOOT! [“DOOOOOOOOOOOT!!!†in original] and they make way.
Wouldn’t a Shortbus-style flash work just as well?
