While getting on the gas coming out of a downhill 25-mph right turn at a semi-rural intersection I heard a mad hiss as the cabin filled with white clouds. Instantly blind, I immediately pushed in the clutch, killed the motor, and steered toward the guardrail. Took me a minute to figure out what was going on. The extinguisher rolled out from under the seat, and somehow the pin came out and the lever activated itself, fittingly, on a boring surrealist novel a friend had loaned me.