I suspect this refers to a klaxon horn. Horseradish graters (some of them) were boxes with a crank handle, and a cog wheel (thrumming a metal strip connected to

I suspect this refers to a klaxon horn. Horseradish graters (some of them) were boxes with a crank handle, and a cog wheel (thrumming a metal strip connected to the amplifying horn) was a vital part of klaxons. Awooga.