Well the article claims cave is pitch dark, so I guess the invisible part is granted anyway.
Cave-dwelling animals don't just crash into walls all the time, so by "visible" I mean large enough and dense enough to be recognized as an obstacle in whatever navigation system they use.
alt Hacker News
Cave-dwelling animals don't just crash into walls all the time, so by "visible" I mean large enough and dense enough to be recognized as an obstacle in whatever navigation system they use.