The auto-stiffening brush incorporates bristles (or perhaps, Bristlez) composed of shape-changing metal, designed to adopt two primary shapes: a doubled-over, tight "U" configuration when heated; and a perfectly straight filament when cold. Clearly, the "U" shaped bristles will be stiffer than the filaments.

Heat required to enact the shape-change comes from the friction of the scrubbing action. The more difficult and prolonged the task (for example, removing English cricketers from the pitch after Australia's done with them), the more the auto-stiffening brush helps you out by optimising itself for the job. Of course, if you plunge the brush into hot water prior to scrubbing, it will automatically change to the stiffer configuration.