Razor blade

This is something that Samuel Vimes cannot bear anyone brandishing near his face. Much to Willikins' disgust and thinly-veiled disapproval, Vimes prefers to shave himself. However, they have arrived at an arrangement that means Willikins, whilst reading the Ankh-Morpork Times out loud while Vimes shaves, will warn him first before reading anything especially contentious or critical of the City Watch.

Keeping these items sharp is also a fringe benefit of building Pyramids...