This is basically a centred double decrease in purl. It reduces 5 stitches to 1 stitch. I use it in Cailleach-Oidhche to create the owl on the reverse side of the cowl!
1. Slip stitches 1 and 2 purlwise to right hand needle.
2. Slip stitch 3 to cable needle and hold to back.
3. Purl stitch 2 and 4 together.
4. Pass stitch 1 over the new stitch.
5. Slip stitch 5 knitwise.
6. Slip stitch 5 and the new stitch to the left hand needle.
7. Pass stitch 5 over the new stitch.
8. Slip stitch 3 to the right hand needle, then slip the new stitch to the right hand needle.
9. Pass stitch 3 over the new stitch.
The last image shows the decrease on the reverse side of the knitting.