1. look at which end is obvious younger and narrower -- won't work if both sides are the same width
2. look at the wavy part -- won't work if the wave is not prominent
3. look at how the spines are attached to the vine -- won't work if the cutting is more of a triangle than a star cross-section
4. peel back one spine to look at how its fiber attaches to the vine -- will work always but you damage the cutting. Better make this the last resort and only do it to the spine closest to one end.