Sonic gun

The weapon wielded by music master André when the Monster Horse Beastie starts to run amok at Master Payne's Circus of Adventure. It doesn't do much to the MHB, which is eventually dispatched by more conventional means (sword and death ray -- remember that in the world of Girl Genius, a death ray is a conventional weapon), but does make a tremendous racket.

André's use of the sonic gun is one of the things that alerts Agatha to the fact that the Circus is providing cover for lots of low-level Sparks. This is useful knowledge...