The creature was in sight now. Jokval eased through the bushes, making no noise in his approach. The beast was feasting on the carcass of a deer. Jokval raised his bow, the only sounds were that of the monster's gluttony and his arrow drawing across the bow. He breathed in then out. Suddenly the beast whirled. Jokval maintained his position. There was no way a mere beast had spotted his position over 50 meters away. Suddenly a sharp pain in his side threw his aim away from the beast. He glanced down to see a sharp spine of bone. He could tell the shot was fatal. As the world faded to black, he realized why the deer had such great hearing.
Actual Question: What environment would a creature develop a natural kinetic projectile launcher? (No fireballs, venom, etc. the object should kill by going through the thing, rather than poisoning it.)
Bonus Points: Build a creature around the launcher!
Note: I understand this will sound something like this question. But I am asking about the what would make it develop, rather than the would it develop.