If it's dark enough the tips glow faintly like a candle that's just been snuffed out.

You can see the glow in this blacklight photo I took (sorry if it's hard to see, I didn't turn off color correction on my phone). https://programming.dev/pictrs/image/b59c9d6a-d514-4158-bea0-7273eef17437.jpeg

The plant it's growing on is a dead piece of a Mountain Ash/Rowan shrub which seems to be bouncing back from whatever killed that branch.