A random anecdote relating to animal aggression:
When I was in high school, I knew a guy who was a self-taught electronics/computing/musical genius. In his tiny bedroom, as well as the computer and synth, he also had a pair of huge home-built woofer speakers, plus a dozen mega-tweeters scattered about. The tweeters looked like foot-long acorns.
But the interesting bit is how he got the tweeters for almost no money…
Australian farmers have a tendency to get cranky about kangaroos eating “their” grass. But it isn’t easy to keep kangaroos out of a sheep paddock; they’ll just hop straight over normal fencing, and super-tall fencing is prohibitively expensive.
So some dude invented a kangaroo-repellent system that was basically a motion sensor and a very loud ultrasonic screamer (AKA the foot-long acorn tweeters). He tested it out, and it seemed to work; kangaroos fled from it. So, he started production, began to ship to the farmers…and then immediately went out of business.
What happened, is that once they deployed the system in the bush, it would successfully scare off the female and young male kangaroos. Who would then go and report the situation to the nearest alpha male, who would then hop on over and kick the shit out of the speakers. 
