Does one cut it off at ground level or further up the stalk?
How Does One Prune Costus Barbatus
If you're talking about pruning after flowering is done and the plant is starting to die back, you would want to prune at ground level. I think. There's really not very much information on this plant, but based on the plant's appearance, that's what I would do if I had one. You might cut one of the stems in the middle, just to make sure it doesn't grow from such a cut. Did you know that if you don't cut off the flower and allow the inflorescence to bend over when the flowering is done, it will start a new clump of plants from where the inflorescence touches the ground?