Sara could never have known that the pen she happened to borrow from a classmate just happened to be filled with cursed ink, and that the classmate in question just happened to be a desperate ghost who was determined to get rid of the accursed pen at all costs. But these things do happen (this is high school after all). Unluckily, the cursed pen turned Sara’s arms into inky black masses, but luckily, this not only appeared to have no negative effects on Sara’s playing, but in fact seemed to have even improved her drumming skills by a significant amount. Regardless, now Sara makes sure she never forgets to bring her own pens to class.
For at least a thousand years Chinese fishermen have been working with cormorants to catch fish in a kind of enforced symbiosis whereby both profit, though the bird is still effectively working on behalf of the human. The cormorants are trained, and when they go fishing a snare is tied around their throats that is large enough to allow small fish to pass, but prevents larger ones from being swallowed and they are stored in its crop (similar to a pelican’s but smaller). The bird gets to eat its fill as it hunts, but any larger fish are taken for human consumption.