a false cave, a burning bush and a fine realm

When you place the attention at the spiritual eye, a strong vacuum gains your attention just below the eyebrows. It feels quite good.

If you do enough HU occassionally the HU will consume your entire skull, and turn it into a burning bush.

If you get the attention above the eyebrows you can get some fine stream of bliss pouring in… when listening to something like "Tibetan Bells II" by Wolff and Hennings.