You can hear the song from miles away. The song is enchanting in a mild way. Even the plants sing this haunting tune all day. This gives you fair warning to be ready to dance to a different tune. You are leaving your country and entering theirs.
This relic, while of little value against the living, is a formidable tool against the beasts from beyond.
The D’athri took to space in such a way to make Terrans look "gun shy". They can be found in small numbers in and around every space port in Known Space.
Teenagers who run away from home to live in the wilderness may become feral. As they become more and more feral, they gain some supernatural powers (a la Peter Pan - ability to fly, things they imagine come true - possibly quite powerful), but at the expense of their humanity and ability to speak, comprehend complex subjects, etc. Maybe they have a leader: the most feral of them all.
A regression into a fantasy childlike state.