The Hands-of-Blue operatives sent by the Alliance to re-capture/kill River Tam use a "sonic" weapon to kill people (causes internal haemorrhaging?), why aren't they affected by their own weapon?
I don't think it's ever explicitly stated, but three theories are:
- They use some type of advanced earplugs. From the nature of their weapon it would make sense. Although this is my least favorite idea.
- The sonic weapon is a directed sonic wave, so they can point it at some area and not be harmed. They have experimented with this (LRAD), so it is plausible that the sonic weapon is more of a directed area effect.
- They are cyborgs, and therefore immune to the sound waves. One of the Hands-Of-Blue had screws in his head and they both moved jerkily and were very inhuman. I think this is the most likely, just based on the evidence and how ruthless the Alliance was.
All of this is conjecture, and we probably will never know because the show was stolen from us.